Is it possible to launch a local application from an HTML or ASP.NET page?
Not really - imagine a malicious website which launched "format c:" at
random - OK, that's an extreme example, but you get the idea...
Having said that, it's possible to stream a file down to the browser in such
a way that it will open its associated application e.g. a Word document, an
Excel spreadsheet etc.
Alternatively, it would be possible to write an ActiveX control or a Java
applet which could do this - in fact, I've done the former several times for
enclosed intranet systems where the target browser is restricted to IE - but
there are severe security implications of doing this, and would be very
tricky on a public site.
Why do you need to do this, AAMOI?
What are you trying do do...?