Power supply for 7800GT

I'm curious, I'm building a new machine with the following components:
Mobo: Asus A8N-SLI Premium
CPU: Athlon 64 3000+ (Venice)
RAM: OCZ Gold Pc3200 2x512 (2-2-2)
GPU: BFG 7800GT OC
Other: (2 IDE hard drives, NEC DVD burner)
I'm pretty sure I'll need a new PSU as the one I have now is only 20pin (A8N uses 24pin) and 400w (12v only kicks out 17A). The BFG card says it needs 26A across the 12V rail, any chance I can get away with my existing PSU with a 20 to 24 pin converter for a month or is it risky? I want to get one of those Sunbeam NUUO 550W sli certified, but EVERYONE is sold out of them right now, and I don't want to drop alot of cheeze on a PSU right now. Can someone advise me if this PSU would be adequate for SLI in the future http://www.newegg.com/Product/Prod [...] 6817182010

or alternatively tell me any retailers that have the Sunbeam NUUO instock;

or option C, recommend another reliable power supply for under $75 that will meet my requirements (doesn't have to run SLI, just the components above)
Cheers,
-#9

<P ID="edit"><FONT SIZE=-1><EM>Edited by ScrumHalf on 10/20/05 09:44 PM.</EM></FONT></P>