New web interface, old engine

My company has an older MSDOS based program (I'll call it "engine") that we would like to make accessible to internet users.

We are thinking about creating a simple browser-accessible form where the user can fill in a few prompts. Then the input gets sent to the engine that parses it and does lots of calculations. Then it returns a list of items that get displayed on the user's screen in browser accessible format.

We want this to be more of a teaser, so the form can be simple (maybe 2-3 screens with 5-10 prompts each). Also, rewriting the entire engine is out of the question (over 100,000 lines of code) - we don't have time to do that. The parsing routine would be a minor change that we expect to accomplish within a few days. The engine will run behind a firewall.

I am new to web programming and need to find out what language to use to create that form - CGI/Perl? some scripting language?

Any suggestions will be appreciated.