You dont need root access to install DBI in your own directories though you may get warnings if the install tries to add the docs to the Perl doc tree.
perl Makefile.PL Prefix=/pathtoyourdir/ should get round that
I dont see what use followed by require will give you (though that could be me missing something)
Sorry, I meant that as an either/or case, not both in one script.
My point was that using require you can run a series of tests (see Camel Book pg. 205) allowing you to determine points of failure in the import routine more specifically that via a use.