Buttons too big in Vista

Question

I have a C# application we've been installing on XP for a year or more.  We are now testing it for Vista.

It's ok, but the buttons appear about 5 times too big!  It's ridiculous, they take up half the screen.  Why such large buttons?  I don't want to make them smaller because we still primarily support XP where they display correctly.

Has anyone else encountered or overcome this issue?

Many thanks,
StonePiano