There is a jumper on the HDD that would set it down to gen1 SATA. Have you tried that?
Also, with the fans, you might be interested in a standalone fan controller, or better still, a molex-3pin adapter. Would be a much easier alternative to getting a new motherboard.
However, can't do anything with the mem slots. Seems like a very expensive RAM upgrade if you've got to upgrade the motherboard as well.
Personally, if you're not using DDR2, I reckon its time to get a replacement if you need more power. But if you think a new motherboard will solve all your problems, then we'll help you look for one. I don't think we've got your system specs mentioned yet, but raybay seems to know that you're using an AMD....