Strawberry Perl currently will always install into C:\strawberry\ , which doesn't overlap the default directory for ActiveState Perl.
When installing ActiveState Perl, at the third step "Custom Setup" when it asks what features you want, it also shows the defaulted "Location: C:\Perl\" and a 'Browse' button next to that. Click that button and change the location to whatever you want, such as "C:\Perl51001\". You can do that with any of the ActiveState installs.
And as Rob mentions, I also have batch files to switch my DOS window to the desired version: pathperl510s.bat , pathperl588.bat , pathperl561.bat, etc.
rem Add Perl 5.8.8 to path
path C:\Perl588_822\site\bin;C:\Perl588_822\bin;%path%
