OldBloke

The 700va is a good idea if you can afford it. It will give you plenty of time in the event of a power cut.

I've used a cheaper brand in the past and find that I prefer using the software you get with an APC UPS.

It connects to the PC via USB (as well as the main power cable). If you are away and a power cut happens, it powers the PC by battery until it senses that its battery has about five minutes worth of juice left in it. Then (if you are running Vista) it tells the OS to go into sleep mode. That saves the current ram contents as a hibernation file. When the mains power resumes you can switch on the PC and it resumes from sleep or hibernation with all your running apps and their open docs still happening. Even your unsaved edits are OK.

Having a UPS makes it much less risky to set your drives into the better performance mode which uses write behind caching.