I have maintained 2 versions of perl on a box for several years. Interchange required a non-threaded perl and Fedora/RH (in thier wisdom) only distributes threaded perl. Thier threaded perl also has a load of dependancies to system tools. Though none of the tools relied on threads (which makes the least sense of all). My situation has since changed, due to some package finagling, I now only run non-threaded perl, but my distro thinks it's the regular version (advice on the Interchange Mailing List)

It's a pain - I had one in /usr/bin/ and the other /usr/local/bin/. The biggest and most frequent pain (but not the only) was I had to match modules to both verions - which means double installs (which is quite easy to forget). You also have to exclude perl updates in yum.

My advice - ditch one version or if you need to stay really current find a way to compile.