Just a note that Win2003 mainstream support ends next month (7/13/2010). You can still get extended support through 7/13/2015, but this can be expensive and not be a guarantee of a supported fix (which then puts you unsupported for any vendor softwares).
Since you were running SQL2000, it's obviously been working for you to run an older SQL version. Thinking about security & bug fixes, not to mention that most vendors end their support for an OS when Microsoft does,
the OS is a bigger concern.