Just doing a quick search, not really price comparing or anything and using my personal preferences...
Mobo -
http://www.newegg.com/Product/Produc...82E16813128084 - $80
Processor -
http://www.newegg.com/Product/Produc...82E16819115017 - $240
RAM -
http://www.newegg.com/Product/Produc...82E16820145590 - $100
Vid -
http://www.newegg.com/Product/Produc...82E16814161203 - $115
HDD -
http://www.newegg.com/Product/Produc...82E16822148136 - $100
Case+Power -
http://www.newegg.com/Product/Produc...82E16811145079 - $28
Monitor -
http://www.newegg.com/Product/Produc...82E16824254001 - $170
Vista -
http://www.newegg.com/Product/Produc...82E16832116204 - $100
Of course, you can cut back on things like the HDD (e.g. 320 instead of 500) or the processor (Core 2 Duo instead of Core 2 Quad). A couple of the items also have rebates attached, so the final, final price may be a little lower.