If i buy a chip with 8 cores for my windows xp pro desktop, how much am i looking to spend more or less?

No-one can tell you, my friend, as you haven't given the details of which specific motherboard it is that you have. We're not able to check whether your motherboard actually supports an 8-core processor.

Without knowing what mother board or CPU you have now its hard to say...and if you have a "factory" machine its likely you cant make that sort of jump to an 8 core. You would need a mother board that was designed to take an 8 core. then too if your board is an older board with DDR2 ram you would have to buy DDR3 ram. To get the most out of an 8core and ram you would want to use a 64bit OS...if your XP Pro is only 32bit you wont get the bigger performance gain you want you would need Win 7 64Bit That would mean reformatting your hard drive...which means you lose everything on the drive...you would have to back up all your work on a External drive or CD/DVDs. You may have to get a newer PSU depending on what ever ..other..things you put in the machine. In essence you would have to rebuilt the machine...which in turn...be expensive! Then to...8 cores are only good if the programs your using can take advantage of all 8 cores!...Sorry

im assumeing your talking about a cpu...
and you would probly have to get a new motherboard too..
power supply... i don't think u would have to upgrade... unless you plan on buying more fans to keep this beast 8 core chip cold...
and yes you would have to install windows xp /vista/7/8 all over again.

A chip? You mean motherboard, I suggest i7 8 core but it costs like 300-500 dollars :/ Also you would need to upgrade to windows 7 cuz xp is outdated. You would also need to buy more ram and fans to orevent it from overheating.