hey there folks
im back
I don't remember you, but welcome back anyway.

im about to sell my two computers and i was wondering if i should get a laptop from alienware or some place or if i should build myself a Pentium four desktop
Build your own if you have the time. You will save a lot of money and can get exactly what you want.
The single core P4s suck. They are slower than equivalent A64s across the board, sometimes by significant margins, and don't have any price advantage. They also run considerably hotter and consume much more power, if that matters to you. For gaming, getting a low end A64 venice and overclocking it is probably the best option.
and i build myself a desktop, ... how much ram , video card and what brand of motherboard should i get?
1GB is about the minimum for modern games. Some newer games like BF2 struggle with even that and need 2GB. Just get some value 2.5-3-3 latency stuff, although there are some 2-3-3 rated sticks at comparable prices; the more expensive stuff isn't worth the small performance gains.
As for video cards, if you have the money and a good monitor with a decent max resolution, then get a 7800 GTX. Nothing touches that card and the prices have fallen to about $500 now. The eVGA KO one is probably overall the best, although Leadtek is coming out with one that might be a bit better. Otherwise, get an X800XL or one of the cheap X800XTs if you can find a good deal on those.
For motherboards, the DFI nF4 ultra-D board is still the best one overall. Asus boards are a bit more reliable and good choices overall but tend to cost more and aren't as good overclockers. MSI makes one with a very good onboard sound chip, if you want to use that. Epox also makes one that is quite close to these but is priced lower. Unfortunately, there still aren't any boards with that new ULi chipset.
and whats this thing about Socket "T" and the "Dual Core" processors about?
would there be any difference from a "single core" presscot compared to a "dual core" smith field?
Socket T is just the new Intel CPU socket interface. All modern Intel desktop CPUs and motherboards use that.
Dual core helps a lot for multitasking and certain types of programs (mainly rendering and math computation stuff), but won't make any difference in games for at least another year. The PDs are slower but less expensive than the Athlon X2s; the lower end ones are a pretty good buy, although their motherboards are more expensive.
or if i should get a laptop
please tell me what kind and from who...
Only get a laptop if you need the portability. They have gotten better but still lag behind desktops for games, both in performance and price.