well for me i would get the mac, if its a desktop you want then i would get the imac 20" with
intel dual core 2.13GHz processor
2GB of DDR2 SDRAM
250GB hard drive
ATI Radeon x1600/256MB Grapics card
and any extra's that you want.
Without any extra's on that config. above it comes to $1749 which is about £916
If you wanted to go for a PC i would personally go for a Mesh
The one i would reccomend would be
This one
TBH i think you should get a Mac And if you really really want you could run windows via Bootcamp...the best of both world
hope that helps
EDIT: also whatever it is that you decide to buy please make sure that you get a nice big moniter
IMO they almost make a desktop complete, the bigger the res. i think the better
i would go for 19" and up.