Tough call... I am not really excited that you might invest $250 - $300 or so in good DDR RAM.... If you decide to get only the Opty, then I would say that's a good plan, since that's a significant upgrade over your current CPU.
I would at least go for a DDR2 based system (either Core 2 Duo or AM2) if you upgrade now. Some really good DDR2 RAM is this Crucial kit
for $230.00. It's DDR2 667, but can overclock really well (same chips as several DDR2 800 kits)
Add an AM2 X2 3800+ for $160, or an E6300 for $180 and a motherboard in the low $100 range. (AM2 might be found a little cheaper, Core 2 Duo board will be a bit above $100).
Thus, for $500 you can go AM2 or C2D and be at least a bit future ready.
I would do that over investing in 2GB DDR RAM and the Opty (which will easily cost $400 combined)
PS: I think QuadFather will simply be too expensive (around $1,000 for a pair of CPUs)...