What you're looking to write here isn't a translator. It's a compiler, and this is a nontrivial piece of work. You're lucky to some extent that VHDL and Spice are pretty close in terms of features (sorta) so it's less of an issue than a PL/I to Fortran converter, for example. Still, this is a Tough Problem.

I'd take a look at Parse::RecDescent, Parse::YAPP, and the command line tools lex and yacc. A good compiler book wouldn't be out of order either.