when you say a computer shop loaded xp for you does that mean you purchased windows xp with the actual cds and everything and they installed it for you or do you mean they charged you to install their own copy of xp with a known blacklisted serial number?
if the shop charged you for a pirated xp, i’d be VERY upset with them.
what operating system did the computer come with? sometimes you can purchase the discs from the manufacturer for a reduced price if you already have the serial number or product code or whatever. this code is usually located on a pretty little shiny sticker somewhere on the outside of your computer case.
if you have no serial and no recovery partition or recovery discs though it looks like you’ll have to buy a new copy of windows.
…or download linux.
if you have no recovery partition as CCRomeo mentioned, it seems like the only step at the moment is to buy an OS and install it yourself. this way you can be sure you’re using the serial number that came with YOUR discs.