Sorry if the simpleness of this answer insults you, but I find the simple answers are sometimes the ones that work.

Have you tried pinning the folders to the taskbar or locking the taskbar (if it's unlocked)?

 

I wouldn't put it past some of the people here.

 

Actually, they're already pinned and the taskbar is locked, so no dice there :?

 

This is from the link that Sacro posted, there's an option to drag items within groups. Did you try this already?

 

Would creating shortcuts on the desktop work? Then you could rearrange the links to the folders however you wanted.

 

I just recently purchased Windows 7, but I have yet to install it.

So... I don't know if you can do this: If I need to rearrange items on the taskbar, without actually closing a window, I just right click and 'Minimize to Tray', then click the items in the tray in the order I want them on the taskbar.

Also, since the phrase has been used, I am now compelled to post this LINK (mind the volume). :awesome

 

Okay, so I got the program from Sacro's link, and it allows me to sort my folders using right click. That's good enough for me, so thanks guys!