1. computer to stay away from... i have never had a problem with dell, i know Aza had problems with Toshiba, but that was for with the place he bought it from, future shop.
2. you could always just get a wireless router that has ports in the back for wired connection.
3. Wireless N or 802.11N is the next generation of wireless after wireless g (802.11G). G is 54Mbps and N is 540Mbps with a greater range. but since they haven't finalized the standard for N, everything out there is just draft, so i will change.
4. for what you are going to be using it for, yeah, 2Ghz and 1Gig of ram should be enough.
5. 15.4 is normal. easy to read stuff off of it.
6. If you can find a store that will sell you XP, yeah just reformat it with XP.