Agreed with the guys above on the motherboard...don't bother with a new board unless you plan to replace your CPU and RAM as well. It's just not worth buying into a new 775 motherboard at this point.
As long as your PCIe 1.0 slot is 16x, you're not going to be holding back your card too bad (it would be about on par with PCIe 2.0 8x). So, I'd say keep what you got.
The SSD would be a good investment, IMO. It would be a huge improvement over your 7200.11 disk. You can keep your old hard drive and use it for documents or other large files. However, I would wait just a little bit longer...from what I understand, it looks like there are some new SSDs out or coming out soon (Vertex3 for example). So, there should be some adjustments in the prices of the stuff currently out. Just something to watch for...I know it sucks to buy something only to have the price drop a few weeks later.