The only thing there good enough for new videogames is your OS, im afraid, that computer is hella old, and partial upgrades will end up in bottlenecking and in a bad performance, I'd tell you to save money, but since you cant, this is what I'd recommend:
1st of all, buy your pieces on internet and make the computer yourself, it's not hard if you follow the instructions, and it might even be funny and exciting. You can't afford to pay 50$ just to get it done, im afraid.
VGA:
http://www.newegg.com/Product/Produc...82E16814130328 179$
Quite decent for its prize and easily upgradeable, you can purchase another and make them SLI if you upgrade your mobo also later on.
MOBO:
http://www.newegg.com/Product/Produc...82E16813128059 89$
Pretty good mobo, gigabyte delivers for sure, and this piece, being a bit old, is madly cheap for its quality.
Processor:
http://www.newegg.com/Product/Produc...82E16819116070 92 $
This one will overclock decently and will give you enough speed not to bottleneck the system, while keeping it cheap.
PSU:
http://www.newegg.com/Product/Produc...82E16817341010 79$
Pretty good PSU, will be enough to get your processor at 3-3,2 GHz with ease and saving a lot of money on that
RAM:
http://www.newegg.com/Product/Produc...82E16820134046 38$
Good ram for its time, right now it will work decently on your rig, and you can upgrade to 3 or 4 gb whenever you want
Case:
http://www.newegg.com/Product/Produc...82E16811156053 23$
Will do the job
Hard drive? Use the one you already have at the moment and sound card, the one integrated.
Hope it helped.