you can boot from the XP cd no problems. But make sure you download the drivers for your chipset and (most importantly) network card/broadband modem prior to formatting it, as if you havent got your network card drivers you'll be fucked as obviously cant get online and download them

You'll probably be able to grab them off the advent website, or if you look in device manager you'll see what devices you have and download them straight from the chipset manufacturer (e.g. intel, SiS, nvidia etc)

With it being an advent pc it's most likely just got clone hardware in, so take the side off and see if you can see any motherboard model numbers (ones that start with MS- xxxx for example, as that'd be a micro-star) then also try the motherboard manufacturers website

Download them prior to formatting and burn them to CD for use afterwards. Remember if your planning on putting them on USB drives you'll be fuckin lucky if you'll be able to retrieve them without your USB controller drivers installed (which would be on the usb drive )