In today's searchWin200 developer tip, the apcompat.exe program was recommended for helping to get legacy applications running in the Windpws 2000 environment. Microsoft has a full suite of documentation and tools on their MSDN Web site that go even farther than this one program does.
A common compatibility issue's whitepaper, and several documents on best testing practices and tools to help fix compatibility issues are included.
One caveat -- the current release of these tools will not work with W2k SP2. An updated version that will work with SP2 is still forthcoming.