You have to start with the top-tier talent that delivers enterprise apps in Visual Basic 6. They need to know VBA language inside and out. They should implement templates for what every primitive does in terms of stacks, registers, and/or control flow (esp jumps). This includes common representations, type system rules, binary interfaces... you name it. Everything one needs to know to parse and implement VBA files along with reference implementations in VBA.

Then, you pay a LISP consultancy to implement that as a DSL in Racket or Common LISP that runs during development and outputs portable C for production w/ frameworks like WxWidgets and/or NPRS runtime. They should be able to throw the whole thing together in under a year. :)

I really don't know anything about VBA or VB, but they're very similar to each other, right? FreeBASIC is AFAIK also pretty similar to VB, but draws inspiration mainly from C++, and has an experimental backend that emits LLVM assembler/IR.

http://www.freebasic.net

Man, I can't wait to see the comments THIS gets