For 1 and 4. I would recommend what razor_gt mentioned. It will do what you're doing just fine.
2. The only difference i would say there is the price. AMD system are a little weaker than intel but then again, for what your doing you wouldn't notice the difference between them so the cheaper AMD will be just fine.
3. If you're going for 4GB of ram, i would say go after 64bit os like XP 64 or Windows 7 64. 32bit OS will not see all of that 4GB. It will only see around 3GB.
Hope this helps so far and welcome to Tom's!