barbone kits, like daisy said, are case, mobo, and PSU. you will need to purchase an AM2 socket proc:
http://www.newegg.com/Product/Product.aspx?Item=N82E16819103257
http://www.newegg.com/Product/Product.aspx?Item=N82E16819103256
and a videocard:
http://www.newegg.com/Product/Product.aspx?Item=N82E16814127284
http://www.newegg.com/Product/Product.aspx?Item=N82E16814130332
http://www.newegg.com/Product/Product.aspx?Item=N82E16819103256
and a Hard drive:
http://www.newegg.com/Product/Product.aspx?Item=N82E16822152107
and an optical drive:
http://www.newegg.com/Product/Product.aspx?Item=N82E16827136144
RAM:
http://www.newegg.com/Product/Product.aspx?Item=N82E16820231044
and trust me, 250w psu is pathetic, and if you want any video card(like the ones i mentioned), your gonna want a 500+:
http://www.newegg.com/Product/Product.aspx?Item=N82E16817153059
i think thats pretty much it and you might want to dual boot linux and xp or you might not get drivers, allthough you shouls be able to download them. IMPROTANT: when you install a CPU, it must have thermal grease or the cpu will fry!!! heres a link to some thermal grease:
http://www.newegg.com/Product/Product.aspx?Item=N82E16835100301
all you need uis about a pea sized drop on the cpu and then evenly spread it around.
of course, you dont have to buy those parts, but they are all good, and when buying a GPU(video card) make sure not to purchase from zotac...they didnt givee me my $40 rebate...
RAM, make sure you buy from a brand name, like G. Skill, patriot, OCz, kingston, crucial, corsair...
these parts are all gonna work the the bare bone you chose. if you geta differnt one, MAKE SURE THAT THE PARTS WILL WORK WITH THAT STUFF!!
also i dont know hwat your budget is, but i added about 300-500 dollars to the barebone...
I really hope i was able to help i spent at least an hour finding these parts...but it was fun. always is and has been. whatev u decide to do, have fun, and remeber, im not resposible if somthing DOES blow up in your face

HAVE FUNN!!