Thanks for the reply,
i have read the article on migrating the code to ArcGIS 10.
My problem is that i don't want to build two versions (in two separate computer) of my application because some users have ArcGis 9.3 and some ArcGis 10.
I have a vb6 application and there's no problem, the same exe run with ArcGis 9.3 and 10.
There is no way to use the same exe with ArcGis 9.3 and ArcGis 10 with vb.net ?