I am confused with your model. If it is a Compaq 1800 you can get the service manual [http://h10032.www1.hp.com/ctg/Manual/c02008065.pdf|from here] As for running Win XP or Win 7, I don,t think that would be a good thing. The CPU as well as the memory requirement are most likely not met for an upgrade. This is not to say it can't be done, but you really would have to customize XP to a bare minimum. Considering a version of Linux for this computer might be a better idea. Hope this helps, good luck.