It will leave v.X intact.
If you're nervous about your preferences, etc., one way to keep the two
suites separated is to create a new account in OS X and only run Office
2004 in the new account - that way 2004 preferences won't be installed
in your main account's ~:Library
references:Microsoft folder. You can
use the Shared folder to access the same files in both versions.
Since I do a lot of testing, and need to keep installs clean, that's
what I do - v.X only runs in one of my test accounts. Takes about 10
seconds to switch.