There has been chatter about how to use Legacy VB with PDA's, without much real promise. A couple hype products (Crossfire and what not), but actually finding a working VB app on a PDA has been ultimately elusive. My strongest suggestion, is to look into VB.NET, with the Compact .Net Framework, which will allow most modern windows based PDA's to run your app. There is a site that appears to hold some promise... but the language is entirely it's own beast (ie: it's not actual VB at all.) called NS Basic . The product impressed me, but was overall not free of charge, which I find to be a big deal (not that .NET is free of charge either, but you know what I mean).
The only other possibility that I can see as an option... and believe me, this is quite the far shot, would be to see if the PDA can run ActiveX controls. You would most likely need to run it through the Web Browser of the PDA. If, and this is a very big if.... if it can run ActiveX controls, then you could basically port you application into an ActiveX control (another type of project instead of standard EXE) and embed that into a web site (unless it will just run natively which I doubt). Let me know how it turns out.