Most likely, they'll be looking to evaluate two things:

1. That you really do know the things that makes you a good candidate for the job in question. For example, if you're interviewing for an ASP.NET job you'll be asked to display knowledge of things like Postback, Sessions State, and how to reference a class library from the ASP project. If you're applying for a VB6 position, you can expect to be quizzed on things like referencing third-party COM components, ADO recordsets, and perhaps making API calls.

2. Technique and style. A programmer will probably look at your code to see how you solved the problems put to you. Was your logic brute-force, or did you craft a more elegant solution? Did you use the best locktyps for your ADO recordsets, or did you open everything with adOpenKeyset and adLockOptimistic? Did you set your object references to "Nothing"?

Those are the things I've looked for when I have evaluated candidates code samples.