I'm thinking for that price range, AMD are your best shop for a mobo and cpu.
Have a look at the Athlon 64 x2 range, these go with the AM2 or AM2+ chipsets which amd have on offer. You can get quite a cheap and overclockable combo here.
Ram really wont set you back that far, you can get 2048mb of high quality ddr2 ram for less than 50euro.
The PSU is what you need to be careful with, cheap psu's can come back to haunt you.
Go with nothing less than 550watt I think.
If your looking for specific items:
Case : APLUS Case Qubic [35euro]
PSU: AXP Powersupply ATX 630W [52euro]
CPU: AMD Athlon 64 X2 5600+ [105euro]
Mobo: ABIT AX78, AMD 770, Socket-AM2+ [60euro]
Graphics card: Gainward GeForce 8600GT 512MB GDDR3 [76euro]
You can definetly get these components cheaper elsewhere, this is Ireland I'm living in (most expensive country in europe for a lot of things, second most expensive for the rest). I reckon you can save 100 dollars on these prices in total by shopping around.
This all comes to 320ish euro, which is just 500 dollars. You need to check the cruicial memory selector if your going to buy more ram. http://www.komplett.ie/k/kc.aspx?bn=10232
Of course this is all assuming you've got a monitor/keyboard/mouse lying around.
Post edit: Oops I forgot a optical drive didn't I...Edited by waynex - 6/1/08 at 3:31am