It's not a supported operating system. We don't program for it, we don't test on it, and we don't provide technical support for it.
Any idea if AE CS5.5 will work on Windows Server 2008?
Very likely not. WinServ 2003 isn't even a full Vista and as Todd already said, absolutely not supported in any way. I'm sure there is some convoluted hack involving installs of .NET, MSVC runtimes and other stuff including manual registry edits and registering DLLs via regsrv, but this may be a rather nerve-wrecking experience, so I don't think it's worth the trouble...
Are there any plans or ongoing development at Adobe to support AE on WinServer?