What you need is a friendly PC guy who will fit a new mobo and ram with your current cpu for free, failing that one who will reassure you that you can fit it np
If you cant find the guy and you chicken out of DIY then save your money until you can afford an athlon64 barebones system imo. I have done some research into cpu/mobo/ram types and prices recently (I am upgrading in a month and a half hopefully) and I reckon bottom-range athlon64/good mobo/cheapish ram is where the real bang for buck is. Athlon64's arent dirt cheap but the 3000 and 3200 are pretty reasonable - and good fast 'forward looking' chips (64bit windows is coming...) Radeon 9800 is a nice value/power card to go with it - and if you want to upgrade gfx later on the cpu/mobo will drive something much more powerful too.