Since I discovered I really can't play certain new games on my pc anymore, (tomb raider underworld being one of them) because my processor is a serious bottleneck, athlon xp 2000+ 1.67GHz, and TR underworld needs 3GHz, it really is about time to upgrade. But it means I have to change my mobo to be able to upgrade the cpu. However, it's not like I play a lot of games like crysis, etc that need super fast processing, and all other things I do on my pc run acceptably for the most part. So on that basis, I really don't want to spend a lot of money, and don't require links to overly expensive top of the line stuff. Just enough to allow games to run well. I'm tryng to keep within a budget of around £300 max if possible. But it would be cheaper to build with components than buy a whole new pc, wouldn't it? Thinking of keeping my computer case, which is basic but should be ok, unless you think I need a better or bigger or more airflow designed one, depending on which processor I buy. I have a 550w psu in it which would be ok to use wouldn't it?
I'm thinking of buying:
1) CPU
2) MOTHERBOARD with sata, pci express and agp and maybe 2 ide slots if it exists,
3) 2GB of whatever type of DDR ram I need, DDR2 or DDR3, I've no idea.
As far as graphics card, tomb raider didn't fail on that, it passed by one notch over minimum pass mark. It's a 7600 GS agp, with 512mb onboard. If I have a pci express mobo, I'll be ready for a gpu upgrade, but for now, my card might be ok.
Not sure whether I can install my 2 IDE hard drives from my pc, one of which has XP installed, and save myself having to reinstall windows to a sata drive.. for now anyway? Would my old ide drives work as soon as installed into a new motherboard? Is there such a motherboard that does sata and 2 ide drives? Alternatively, I could buy a cheap usb enclosure to house the IDE drives and buy a sata internal drive and install windows?
Anyway, don't worry too much about the above questions yet, my MAIN question is.. which 3GHz processor, Intel or AMD? How important is L2 cache? I've selected a few here from overclockers, all AMD, all great prices and below £100, would any of these do me to take care of the latest demanding games and be somewhat future proof?
This first one looks like the best to go for, especially at the price I want to stay at compared to an intel equivalent which seems to be more expensive? Apparently it has 7.0MB L2+L3 Cache. Is it essential, or would lower amounts of cache also be sufficient, like 1 or 2MB?

AMD Phenom II X2 Dual Core 550 3.10GHz Black Edition (Socket AM3)
http://www.overclockers.co.uk/showprodu ... =6&subcat=
EDIT: apparently this one is highly recommended, supposed to be amazing chip for gaming:
AMD Phenom II X3 Tri Core 720 Black Edition 2.8GHz (Socket AM3)
http://www.overclockers.co.uk/showprodu ... =CP-238-AM
AMD Athlon II X2 Dual Core 245 2.9GHz (Socket AM3)
http://www.overclockers.co.uk/showprodu ... =CP-251-AM
AMD Athlon II X2 Dual Core 250 3.00GHz (Socket AM3)
http://www.overclockers.co.uk/showprodu ... =6&subcat=
AMD Phenom II X2 Dual Core 545 3.0GHz (Socket AM3)
http://www.overclockers.co.uk/showprodu ... =6&subcat=