Could a vbs (VBScript) language file be added? It's very close to VB, but it'd be nice if there was more function highlighting.
If you know a little php, it would not be hard to make it yourself. See section 4 of the documentation that comes with GeSHi.
Otherwise, I'm not familiar with this language and so could not write the language file myself. If you could find someone with a little PHP experience and who knew your language, you could get them to write it.