The problem is that you now have two programs that can be invoked under the name perl on your system, and the two are largely incompatible when it comes to binary modules like DBI. I fear you might even have broken your Debian installation by installing the new Perl 5.8.7, as Debian apt-get is written in Perl and relies on modules that Debian does not make available via CPAN for other versions of Perl. I once ruined a Debian system by replacing the system Perl with a self-compiled version which didn't follow the same setup as Debian.
If you still can, try to untangle the two versions of Perl and make sure that /usr/bin/perl points to the old Debian system Perl. If that doesn't work, many of Debians utilities will be broken for you, mainly apt-get.
Personally, I install all my "private" versions of Perl under /opt/perl/ now, with a PREFIX=/opt/perl (in the Makefile) and with the explicit version number in the path, so all my Perl versions live in completely distinct directories.