Ok, well here is what I can do for 600 USD. You may not be able to get these parts at these prices in other countries, however. AMD Athlon 64 X2 3800+ 2.0GHz Socket AM2 Dual Core Processor - Retail at Newegg.com - $149.00 ASUS M2NPV-VM Micro ATX AMD Motherboard - Retail at Newegg.com - $84.99 OCZ Value Series 1GB (2 x 512MB) 240-Pin DDR2 SDRAM Dual Channel Kit System Memory - Retail at Newegg.com - $84.49 ($76.49 after rebate) HITACHI Deskstar 7K80 80GB 3.5" SATA 3.0Gb/s Hard Drive - OEM at Newegg.com - $42.99 SAPPHIRE Radeon X850XT 100106L Video Card - Retail at Newegg.com - $119.99 NEC 16X DVD±R DVD Burner Black IDE/ATAPI Model ND-3550A - OEM at Newegg.com - $28.99 Antec SmartPower 2.0 SP-500 500W Power Supply - Retail at Newegg.com - $69.99 Sunbeam IC-MX37-BK Black Computer Case With Side Panel Window - Retail at Newegg.com - $27.99 That equals $600.43. Now, that doesn't include a monitor, keyboard, mouse, or speakers, but I am assuming that you have those. If not then you can get a single core processor, like a 3800+ or 3500+ (I have a 3500+ and it is wonderful), a different video card, like an X700 Pro, and maybe if you get really stingy 512 MB of RAM. I would be glad to help you with any tweaking of this list.
Max is right on, it's very possible. Now I'm not really sure where you would order from in Srilanka but in the States newegg is the way to go. The 3800X2 is great but if you can't quite afford it I could definately see going with a standard 3800+ or the 3500+ like Max suggested. You really do need 1GB of ram though, I learned that the hard way. I'm assuming you're getting this with the intention of playing newer games so a X850XT is a great choice, they're not too quiet but the can still max pretty much every game on the market which is a conforting thought for only $120 or so. Just keep in mind this doesn't include shipping either so you'll have to figure about $50 for that as well unfortunately. The harddrive is your own person preference as 80 is fine for some but dinky for others. Concidering how cheap they are these days I'd look into a a Segate Barracuda 160Gb drive for about $58 but that's just me.
$600 is possible, but not in Sri Lankan Rupees. If you mean $600 USD, then, most certainly, you can build a nice box.
The only real problem that I have (well I have one more) with your setup max is the motherboard. It has onboard video, which is utterly useless for gaming, and although I understand it won't be used, it still is a performance hog, even when disabled, not to mention you gotta' pay for it. The other problem I have, is with the hdd, but it's more personal than anything else. As a few may already know, I only buy Western Digital hdds, not because they're faster, not because they're quieter, but because they've been much more reliable to me, and to me, the number 1 priority in a hdd is reliability. The sexiest thing in that setup is the video card of course. A $600 pc with an x850xt is quite appealing to say the least. Oh and ranidub. Why the sad look on your face ? You're getting yourself a brand new pc, that's the most exciting thing a guy can ever dream of. Isn't it guys ?