My recommendation is to not remove CS3 at all unless you need to for space reasons. I have CS3, CS4, and CS5 on the same machine. It’s handy in a lot of cases.
If you must remove CS3, though, you are right to say that this should happen before you install CS5. The other order has the potential to cause problems.
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Todd Kopriva, Adobe Systems Incorporated
putting the ‘T’ back in ‘RTFM’ : After Effects Help on the Web
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