Your specs are ok...
I'd seriously consider adding at least another 4 gig of ram to get to 8 gig at the minimum...add 12 gig if you can...to get to 16 gig, provided your MB will support 16 gig. That's probably the cheapest and BEST thing you can do right now. Consider upgrading MB, CPU, and memory later...
I'd install Win 7 64 on the Raptor (10,000 RPM) and uninstall anything that you won't use (games, etc...) then install Sonar X2, which won't leave a lot of space on that drive, but should be enough...Sonar and VST's only - not instruments...then install all instruments to
one of the Seagate Barracuda's (and whatever other minimal programs you need) and use the other Barracuda for projects...and upgrade the Raptor to a 120 or 128 Gig(at least) SSD when you can...they are getting dirt cheap now...
That's what I would do....
I put Win 7 and Sonar on my 128 Gig SSD ....instruments, etc.. to my 7200 320 Gig WD Drive...and everything else on my 500 Gig 7200 Seagate drive...
I will soon be getting at least a 240 Gig SSD....which will replace my 128 and I will use the 128 for for instruments etc....as they are getting more and more SSD capable. The other drives will be used for projects and storage.