Buying a New Computer ... Which Manufacturer?

[dweeb]

hello, all. i'm planning to buy a new computer in the next few days (i'd prefer to build one myself but i'm using my Dad's money and he won't let me!) so i come here, seeking advice.

generally speaking, are there any manufacturers you'd avoid? and which ones would you recommend?

i've always heard good things about Dell, HP etc. but all the suitable Dell systems insist on "Intel Viiv" technology which is only compatible with Vista apparently (which i haven't heard good things about)

if you could recommend me a rig, that would be great. i have a budget of ~£600; as for my requirements, i like to multi-task (alt+tab when i shouldn't), i like to play RTS games (Rome: Total War) and i like to listen to music when i'm doing all of these things (using Winamp, or whatever)

basically, i'd love a system which runs modest programs "smoothly" without groaning and lagging for ages!