I have a UI tool button, I would like to get and use the existing function (select elements tool) in Arcmap when I activate this button, does anybody know that how to call the existing function using Vb arcobjects ??
You can use the ArcMap Commands, eg.
Or, check out this forum post to grab elements on mouse up event.
Not sure if I understand you correctly, but would it not make sense to explicitly GET the tool you want...just in case the user has not selected it? It's OK to set it if it's already set.
Note that ArcID.PageLayout_SelectTool is for ArcGIS 10, in 9.3 it was Select_Elements I think.
Hope this helped.