<p>I have a home-spun 2000 lines VBScript script, that has become progressively slow with each additional code I add. It was created as a private debugging aid and now that it has become really useful. I want to polish it and ship it along with our product.</p>

<p>I thought I could speed it up by compiling it and making it an EXE. Furthermore I want to have a user interface for my tool, which might be possible once I use the extra libraries that the compiling platform might give me. I'm also considering extending the script by calling <a href="http://en.wikipedia.org/wiki/Windows_API" rel="nofollow noreferrer">Win32</a> functions for whatever missing functionalities I require. </p>

<p>I have VB 6.0 or I can buy an external compiler. But I also need the created program (not the compiler itself) to run fine in Windows Vista. What are my best options? </p>

I would recommend downloading Visual Basic Express Edition (
http://www.microsoft.com/express/vb/
) and port your tool to VB.Net. However, that approach has one drawback - your program will be dependent on .Net. For the most part that shouldn't be a big problem, as by now most machines should have .Net 2.0, still it's better to keep it in mind.
I would stay away from VB6.0; however, aside from VB.Net I don't know any other good Basic compilers you could use.