need advise

i have gotten my hands onto a oldish desktop from a freind who just got a new comp. (he isnt verry techno-savvy so he has no use for it) i want to rebuild, upgrade and generaly pimp this thing out. what parts should i start replacing first, and how much do they generaly cost? im planning on making this into a gaming computer and maybe try selling it at a profit (probably not). i plan on slowly replacing just about every part, its all pretty dated. im sure it has a few viruses (he wasnt carefull and im sure he used it for porn) incase that has an impact on you answers and i may be reinstalling windows just to get past that. any tips or suggestions are welcome. almost forgot, the most hardware stuff ive done is upgrading ram, but ive taken apart and put back together a few comps.

 

If it's an oldish desktop, it probably can't be updated to the scale you want. Depending on the specs, it probably has older memory (limited to update and expensive). The motherboard probably won't be able to be upgraded to over 1 GHZ throughput. (Again, don't know the specs, so can't give a qualified answer). If you post what the specs are, you'll get more answers, but don't hold your breath for upgrading an ancient dinosaur.

 

could i just replace the mother board and go from there?

heres some specs from dxdiag, nothing else looked like it was talking about hardware.
Processor: AMD Athlon(tm) Processor, MMX, 3DNow, ~1002MHz
Memory: 768MB RAM