I recently returned from an amazing hike in Torres del Paine and had a lot of trouble finding info before we left, so I hope that some of this information will be helpful to you!
Puerto Natales is the town closest to Torres del Paine. You can rent gear/tents/pretty much everything there.
Getting to Puerto Natales
The most common ways to get to Puerto Natales are either to (a) fly into Punta Arenas & then take a bus up to Puerto Natales or (b) take a bus from El Calafate to Puerto Natales.
If you choose (a), there are 4 bus companies that run several buses daily (at least during high season, starting in November) up to Puerto Natales. The bus stations in Punta Arenas are open until 10 p.m. so you can buy tickets anytime before then. If you arrange bus tickets in advance, I believe the bus can pick you up at the airport and take you directly to Puerto Natales - however as I said, this is only if you arrange in advance.
To get into Punta Arenas from the Punta Arenas airport is about 8,000 chilean pesos.
Getting Ready for the Hike
We attended the 3 p.m. talk at Erratic Rock - this talk will let you know everything you need to know about the route, what to rent, what to eat, what to expect, etc. I would highly recommend it.
After attending the hike on a Friday afternoon, we decided to take our time and begin the hike Sunday, as opposed to Saturday, which we had originally planned. We just wanted more time to go to the grocery store/rent gear/rest up.
Everyone we met had rented gear from different places. Shop around and see which store has the price you want!
One thing I would definitely recommend is to rent hiking poles. These saved my (and many other peoples') knees on the steep ups & downs.
As the 3 p.m. talk at Erratic Rock will advise you, you want light, quick, easy food.
For breakfast, we had oatmeal with dolce de leche & coffee each day.
We never stopped for lunch (too hard to start again) but we took lots & lots of breaks and ate trail mix, granola bars, salami, cheese, crackers, cookies, candy, etc. You will be starving. Bring a lot!!!
For dinners, we had two pastas, one risotto and one soup. Check the cooking times on the items that you buy - one of the pastas that we bought (stuffed) required 15 mins in boiling water, which used a lot of fuel. (or, just bring extra fuel - which i would recommend anyway.)
We also brought one small tetrapack of red wine for each night. It was a nice treat at the end of the day.
Bus to Torres del Paine
You can book bus tickets through your hostel or through your gear rental place up to Torres del Paine. There are several bus companies that all head out at 7:30 a.m. & 2:30 p.m.
We did what Erratic Rock suggested in terms of route - a classic W route from west to east. We camped as it's cheaper & gives you more freedom in terms of where you sleep. The campsites are usually in better locations than the refugios, as well.
Day 1: 7:30 departure to Torres del Paine. Arrived a few hours later, had something to eat & got on the Lago Grey ferry at 12:30 or so. Started at Refugio Paine Grande up towards the glacier.
We expected to camp at Campimento Los Guardos that night. The map shows that the hike up from Paine Grande to Refugio Grey is 3.5 hours. This was not true for average hikers like my friends & I. It took us 5 hours with the wind blowing against us, really heavy packs and not being used to the routine of hiking.
We decided to stop early and camp at Refugio Grey.
There is a store there which sells fuel, some food, drinks, etc.
You can also use the washrooms & showers in the refugio.
In mid-November, it was staying late until 10 p.m., which was awesome!
*Note: a fire in December 2011 burnt most of this area of the park.. sometimes you feel like you're in Alice in Wonderland or something. Charred trees everywhere. It's slowly regrowing though!
Day 2: Went back down from Refugio Grey to Paine Grande. Much much easier & quicker on the way back down. Reached Paine Grande and stopped for lunch (in the cook shack there, there are gas burners that you can use for free) and then continued on to Camimento Italiano. It's beautiful. It's right on the rushing stream & you can hear glaciers cracking in the distance. The washrooms there are sick though .. there are only 2 and they're not pretty.
Day 3: Left all of our stuff at Italiano and hiked up into the French Valley. This was my fave part of the whole trip. It was beautiful. The end of the hike up will probably feel like a bit of a push, but it's worth it! Take lots of breaks & eat lots of calories - it's a tough hike.
After getting to the lookout at the top of the French Valley & spending some time up there, headed back to Italiano to get our stuff, and then headed off to Refugio Cuernos. The start of the section is very steep, but after about 45 mins the rest of the hike is downhill. There are a couple of rocky beaches you can stop at. Dip your feet in the freezing lakes - it will make them feel so refreshed!
Cuernos is fancy & has tent platforms for most tents, although we ended up camping slightly uphill of the refugio in a grassy area.
There are showers, washrooms, sinks, cooking areas, etc.
Day 4: Left Cuernos & headed to Campimento Las Torres. Long day & lots of uphill. It was very windy. Once you reach Refugio Chileno you've got another 1.5 hours or so to get to Las Torres. A bunch of our friends headed up to see the torres that afternoon, as well as the following morning.
Las Torres was quite cold (up high) & windy - coldest it had been the whole trip. There's only 1 washroom but it's nice and clean. The stream runs right through the campsite so it's easy to get water!
Day 5: Wake up early (4:30!) to head up & see the sunrise on the torres. Beautiful.
The hike back down to Hosteria Las Torres is easy & all downhill. Caught the bus at 2:30 & was back in Puerto Natales by 5:30 or so. Exhausted.
If you are wondering if you should do this hike, you should. It's one of the most beautiful things I've ever ever seen. Each valley is different and has its own special characteristics. We made a bunch of friends along the way which made the experience that much more fun. My knees definitely took a beating but it was worth it!