Should I have my games on a seperate drive then the OS? and will this improve performance.. I have $80 more to spend and im thinking of either buying a seperate hdd for my games or 2gb extra ram.. Any idea?

Arctic Freezer 7 Pro Aluminium, Koper
Samsung SH-S223F/BEBN S-ATA, Bulk, Zwart
Sapphire Radeon HD 4850 512 MB, PCI-e 16x
GeIL Black Dragon Dual Channel 2048 MB, PC6400, 800 MHz, 4, Kit Of 2
Asus P5Q Pro
Intel Core 2 Duo E8400 3.00 GHz, 1333 MHz, 6 MB, Boxed
Antec Gamersgear Three Hundred Zwart, Geen Voeding
Corsair VX550 550 Watt, 20+24 Pins
Xilence Case Fan 120 Mm, Met 4 Pin Molex 2
Seagate 250GB 7200.10 8MB cache

This is my current system

Buy more memory and make sure you hdd is always defragmented, clean etc..
RAID0 will buy performance if you need to read/write big files at once. Gains in gaming are marginal.
Anyway, make sure your HDD is not close to its limit. 250Gb seems a little tight...