Install them in separate directories. I have six versions of Perl installed on my machine, and I haven't had any problems.

If you want to run a program using a specific build of Perl just replace

perl foo.pl
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with

c:\progs\perl5101\bin\perl foo.pl
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You can do that at the desktop level too. For example, you can create a shortcut called "foo.pl with Strawberry Perl" that executes "c:\perl foo.pl" and a shortcut called "foo.pl with ActivePerl 5.10.1" that executes "c:\progs\perl5101\bin\perl foo.pl".