I'm running Poser Pro 2010 and Poser Pro 2012 at the same time, no problem at all, that would be about the same as running 8 and Pro 2012 at the same time. I'd say Poser 8 and 2012 at the same time should work. I'm running Windows 7 64bit, perhaps the OS you run has something to do with it as well?

Artwork and 3DToons items, create the perfect place for you toon and other figures!

http://www.renderosity.com/mod/bcs/index.php?vendor=23722

Due to the childish TOS changes, I'm not allowed to link to my other products outside of Rendo anymore :(

Food for thought.....
https://www.youtube.com/watch?v=pYZw0dfLmLk