You can run side-by-side. Just keep in mind:
-Your Control Panel settings will only be set up for one ISP or the other,
so, while you can manually invoke the non-selected ISP, the ISP you have
configured to be dominant will work with less effort. (You can easily change
these settings.)
-You will never get rid of every last trace of AOL unless you reformat and
reinstall XP, no matter how you uninstall it and attempt to purge AOL. This
is not a big problem, but it bothers some people.
-AOL has some proprietary features that make it less integrated with
Windows, but this doesn't bother everyone.