Which upgrade?

[d]

I've a rig running an Athlon64 socket 754, 1GB ram and a 6600GT. I'd like your opinion on which upgrade you think is better :

(a) the cheaper option being change my card to a 7800GS AGP

(b) switch to socket 939, get a new mobo, processor, and preferably two 6600GT's for SLi

I'm on a limited budget so .. do the math.
Thanks in Advance.

[assasin]

Why do u wanna buy a socket 939 when AM2 is available.It wud be better if u get urself a new mobo & processor.Dont upgrade ur GPU now.Wait 4 DX10 cards to be launched,see if any card fits ur budget and den get urself a card.