VB -> Perl is probably do-able. VB has fairly simple syntax that can be almost directly transformed into a Perl statement. Of course, except in the most trvial cases, you'll need some way of supplying the library calls the VB code makes. Pretty much any VB API has some equivilent on CPAN, but you need some way of translating it.

Perl -> VB is much, much harder. While a restricted subset of Perl could be done, translating *everything* would be highly non-trivial.