Hey, guys, im one of those lucky guys who will get a dell xps laptop for christmas, so I have 2 choices; the newer core 2 duo dell xps model with 7900gs geforce 256 mb gpu or the older pentium m dell xps with 7800gtx gpu. other than the cpus and gpus their pretty much the same, so which one should I go for? core 2 duo one is 1300 pounds (British), while the older one is 1063 pounds.

p.s. I think the 7800gtx rips a 7900gs anyday...

If you can afford it, get the Core 2 instead. It is based on the Pentium 2, but its much faster and much cooler and much more efficient than any Pentium. As in 30% more efficient.
The 7800GTX is faster than the 7900GS, but only by a small imperceptible margin.