In case anyone cares..... It appears the threaded version of Perl 5.8.0 on OSX is incompatible with DBI. This really bites since you need the threaded version for Apache 2.0.43 and mod_perl 1.99_07. So, on OSX, you are probably better off using FastCGI or, I hate to say, Java Servlets/JSP for dynamic web pages since not having DBI available pretty much makes mod_perl worthless... at least for me.
The distro of Perl I'm using on my OSX box is from serverlogistics.com (aaronfaby.com... there's a link next to Rendezvous on Safari). Since Perl 5.8 is binary incompatible with 5.6.x, you have to recompile all of the XS mods (i.e. Storable)... but with the pkg from serverlogistics, that's all taken care off. I'm unsure if there are similar incompatibilities with threaded Perl5.8 and DBI on Linux... I'll try it out later today. My main Linux box runs Perl5.8 non-threaded and DBI-1.31 works fine. Hopefully, this incompatiblity with threaded Perl 5.8 and DBI gets resolved soon... otherwise Java is looking more like the route to go on OSX... and I really really hate Java. Curt