His @INC included 5.6.1 and 5.005 and those are definitely not binary compatible with 5.8.x.
...but his @INC did not include the arch dirs for 5.6.1 & 5.005. I've had this problem as well, in fact I posted it to the dbi-users list. Nothing was resolved. I've had this happen on FreeBSD, OSF and Linux. I was upgrading the Perl on these servers to 5.8.1. I have a CPAN script that installs the modules we use and it would "hang" when installing Bundle::DBI. On the OSF it actually used all the swap space up. I finally was able to resolve this by moving the */site_perl/5.6.1 to a temp name and installed all the modules in the 5.8.1 tree. Everything I've read indicates that 5.8.x is supposed to only look for the Perl only modules and not use the old XS compiled modules. Maybe there is a XS compiled module in a non-standard dir. The only way I've been able to upgrade is to rename the site_perl/5.6.1 dir. I'm glad someone else has had this problem, I thought I was the only one. I have another server that needs to be upgraded, so I am going to install everything manually and see if can figure out why this is happening.