Hi Lisa,
I'm working on the Mac side, but I'll put in my 2 cents' worth.
I did use the beta on a few machines of varying ages, and experienced some weirdness (disappearing cursor and such, and error messages about missing support items). The "worst" problem I had was when doing a perspective transformation and dragging the handles outside the bounds of the image window. The handles would snap back part way, giving me less transformation than desired. The workaround was to zoom out and stay within the bounds of the window. The release fixed this.
As for using CS3 on older machines, I'm writing you from home on a 7+-year old G4 Mac (dual 533, 1.5 gigs RAM) and CS3 is quite usable on it--maybe even more responsive than CS2. (Don't feel bad for me though; in the office I've got a new quad-Mac Pro waiting to be set up and 100 CS3 Premium licenses!)
I am still sorting out plug-in support. On the G4, I reference my CS2 plug-ins folder, where I have new and old plug-ins installed. CS3 sees them all. In the office on my Intel iMac, CS3 does not (it sees only the CS3-native plug-ins).
You didn't mention how much RAM you have; this could be a factor. Also, Windows being Windows, who knows... Maybe you need a Windows reinstall or other such cleanup.
It is true that uninstalling the beta (which I know you didn't use) and installing CS3 was not a happy experience for a lot of people (check the various forums). I work in IT and also had to fight with it, finally manually uninstalling the various beta pieces after the official Adobe uninstall script did nothing.
So please provide some more details about your system. Do you have a second PC you can try it on as a comparison? Doing so may reveal issues with your main system.
PS: Those are great travel photos on your website!