Either do no warnings 'unitialized'; in the block or do the following:

my @prereqs = qw(DBI DBIx::AnyDBD);

foreach my $prereq (@prereqs)
{
    eval "use $prereq;";
    die "Blah\n" if $@;

    my $v = $prereq->VERSION;
    print "Found $prereq version $v\n";
}
[download]

You could use symbolic references ($v = ${"${prereq}::VERSION"};), but it's smarter to use the methods handed to you. :-)