wasting money on buying windows xp, can any one help me on this ?

ive had this dell dimension 4500 desktop for the last year or so, and ive been pretty carefull about what i install, but note carefull enough. ive had to wipe my drive and install off of a reinstall dell cd that a friend had laying around. now ive got 26 days to find the software it origanally came with. if any one has any ideas at all on where to find the OPs that i am licenced for, pls share them with me. thankyou ,
joshua