You may have wasted your money on buying an XP CD if it has a recovery partition. if you turn the computer on and immediately start tapping F11 it *should* start the factory recovery procedure and take the entire system back to how it was first delivered.
If this doesn't work (or if you want to do a clean install from the CD, which Is how I'd do it) then you would need to boot the computer from the XP CD and pretty much just follow the on screen instructions remembering to delete the main (largest) partition and then recreate it when you get to the partition options.... If you choose this route just take a crack at it... face it if you are wiping the drive anyhow you can't really go drastically wrong, worst case is you'd just have to boot from CD again and give it another go.
The driver are available from the link below...
http://h20000.www2.hp...kId=135&swEnvOID=1093
The required drivers you'd need are as follows (I can't provide direct links due to how HP's site works... but just click download on each page)
http://h20000.www2.hp...135&swItem=vc-75813-1
http://h20000.www2.hp...tem=PSG_I23303-108286
http://h20000.www2.hp...135&swItem=ir-75011-1
http://h20000.www2.hp...135&swItem=ir-91806-1
http://h20000.www2.hp...135&swItem=vc-95687-1
http://h20000.www2.hp...135&swItem=vc-68806-1
http://h20000.www2.hp...135&swItem=vc-87125-1
As I said, download all the above and burn them on CD or put them onto a USB stick so you have them ready for after windows has installed, because until you install them (well at least the network driver) you won't be able to access the internet.... all you have to do with each one in turn is double click on the files, click next/ok a few time and it will install the drivers for you.