[Shaun]

I've got the APC 500 UPS and its great for use with my equipment. Gives me about 24 min from the power going off to the battery failing. Bearing in mind I've got a TFT monitor so it'll use less juice then a CRT. It also came bundled with APCs power chute which can automatically stick your comp into hibernation mode if the power goes off.

Edit - that site listed above recomends:

APC BACK-UPS RS 800VA 230V

Part Number(s):
BR800I

Price: £139.99

However I get on fine with the 500