echo %ERRORLEVEL% ... Is this the proper way to check this?

Yes, I think so, but I'm no Windows expert...

As to the negative return code, IIRC, I was able to reproduce the issue last time with a self-compiled perl-5.8.8 on a Win XP (32-bit) vmware image. Unfortunately, I don't have access to that image at the moment, and any attempts to reproduce the problem on the Windows box I currently have access to (XP x64 SP2, with ActiveState's Perl 5.8.8) have failed so far...

Maybe I'll continue to play with this later. In case I should dig up something of interest, I'll report back.