I've not been studying spanish for too long, but here's my understanding of the difference here
1) Si tuviera dinero no habria hecho esto.
My translation: If i had money I wouldn't have done this
2) Si tuviera dinero no hubiera hecho esto.
My translation: If I had money, I might not have done this.
If my understanding is correct, the (past subjunctive?) (tuviera, hubiera) suggests uncertainty. Of course, this difference may only be apparent because I'm translating too literally again :) The uncertainty in tuviera is covered by the IF, which is why i'm not translating it as "if I might have had money"