I've found it a problem to run two concurrent versions of AS built with the same compiler

I currently have AS perl builds 638, 806, 810 and 817 on this PC, along with Strawberry Perl (5.8.8) and my own MinGW-built perl 5.8.8, and I find no problem running whichsoever version I want (via the appropriate batch file). Main thing is to ensure that the installation of ActiveState Perl doesn't screw with any registry settings (path, file associations, etc.) - which is easily achieved if one installs the '.zip' version rather than the '.msi'. (Faik, it may also be easily achievable with the '.msi'.)

I probably had a bit of luck wrt Strawberry Perl ... the installation of it wanted to screw with the registry, but because I was running as "user" (not "Administrator"), the attempt failed (which suited me just fine :-)
With the '.zip' ActivePerl installations, one is always prompted re the stuffing-up of the registry settings ... and one (naturally) declines the invitation :-)

they're easier to avoid than research

Aaaaah ... I see you're a man after my own heart (so to speak), after all :-)

why not perl5.8.x.dll?

Good question - though it still wouldn't help when it comes to running (say) two different builds of perl 5.8.8

Cheers,
Rob