But you'd be paying a price. While the mac mini won't play the latest games, the fact that Apple have managed to squeeze a decent machine inside such a small, attractive area means is impressive. I think its clear that the target audience for such a product is going to be as a second computer or...
To be honest they are going to be pretty much exactly the same. Have a look at which one has the best bundle and go for that one. If you are interested in the absolute best performance then have a look at the X800XT PE for games like HL2, or wait a couple of months for the X850.
I'm not 100% sure if it is still possible to still do the hard mod on the standard pros but it was possible to use conductive paint and connect two laser cuts next to the core which would apparently unlock the pipes.
If I was you I would buy an arctic cooler rev 4 and just clock the hell out...
www.plus.net
You can get 512k unlimited for £21 or if you can choose to have a download limit and get for even cheaper, down to around £15.
I'm on their 1mb unlimited and can not fault them.
If I were you i would avoid companies like BT, Wanadoo etc.
You say you've checked for spyware what about a virus scan? Also run a couple of anti spyware programmes to pick up some the other may have missed. (Adaware and Spybot search and destroy are both very good.)
If you are willing to reformat, nothing beats a nice clean install of Windows.
The 90nm A64s are very good overclockers as they run cooler than the old 64s, giving more room to overclock. Put a thermalright xp120 heatsink and a decent 120mm fan and you're laughing.
You might get it even cheaper with 128mb. That card won't use 256mb.
As far as HL2 performance is concerned it will run it fairly well at low detail levels.
If £200 is about your budget then I would look at a plain 6800, bit over budget (around £220) but much better performance than the 9800 and 6600.
www.overclockers.co.uk is an excellent site.
If you don't want to save up anymore for the x800 pro, I'd go for the nVidia 6800. While it's not ATi it will perform better than all those above cards in HL2 and you may be able to mod it to 16 pipes.