I am not entirely sure this is possible. I don't have time to research it in google this week (on a long business trip), but if you search google for "Integrate Flash Button with .Net" and find something about it, that might help you solve your issue. If you find code that says it solves it and has problems implementing it, just paste some links in here and I can help interpert whats going on...
I personally don't think its possible, so maybe we can just redesign the button in VB.Net, which is most likely possible. Describe what your button does that is so special that you absolutely want to use it in your VB.Net 2003 project, and maybe I can tell you how to perform the same tasks with your VB.Net controls (if it just looks like something special, we might be able to reproduce the effect in vb.net).
Hope you find a solution, I am going to remove your prior post since this is a double post.