The only problem you can run into is if you have installed programs in the same folder. Avoid that at all costs it will muck up your system. Other than that, no problems.
If you take a truth and follow it blindly, it will become a Falsehood and you a Fanatic.
Shouldn't have any problems....I am currently dual booting with 2000 and ME and haven't seen any. I would definitely recommend separate partitions though, it will avoid most of the potential issues.