Don't just order a pack out of a catalog, call the vendor and talk to their expert. Trying one at your local outdoor store is even better. You need to get the proper tent to keep you dry in the rain. Proper does not mean expensive. The fly must extend almost all the way to the ground, a feature missing in discount store cheapies.
Most backpackers purchase a two-person tent, even if they plan to travel alone.
Expect that two adults in a two-person tent will be very cozy. You can find a complete list of tents and their features in Backpacker magazine, March 1998. Ground cloth for the tent. This protects the bottom of your tent, and keeps ground water off it. This must be totally tucked under the edge of the tent when it rains or water will run between the ground cloth and tent floor and get your gear wet.