Ha ha... Well, there's a first time for everything, right? You're right, though, since Windows 2000 and Windows XP were effectively the same OS, anything that runs on XP well will usually run on Windows 2000 well. I was just making the point that just because it works in MC14, and doesn't in MC15, does not mean that it is MC doing something wrong. Correlation does not equal causation. Of course, it might be MC's fault, but it also might be MC15 exposing a flaw in some other piece of software (almost certainly a driver, if so) that MC14 did not.
But hey... I don't work for JRiver, so maybe they'll be able to figure it out. I'd also just say that you can't really expect them to keep supporting it fully with their new versions, when even Microsoft is dropping support for it in a couple of months. I can say this: I have not seen that same thing with MC15 on any of my Windows XP or Windows 7 builds. I have seen similar screen redrawing issues with software in the past, and often (but not always) it was a buggy video card driver (ahh the old pre-Catalyst ATI days).
But really, I was just making a suggestion that now might be the time to bother with the hassle of the update. Windows 2000 is being pulled from Extended Support in July, though (that means no more patches of any kind unless you pay Microsoft to build one for you, and you can't afford that bill). The current date for Windows XP is April 8, 2014, but I wouldn't be surprised to see that date extended again when we get there.