Might it be that the Java app is drawing everything with custom paint logic and your .net app uses a lot of controls? (usually it's easy to tell from the looks of it, but I don't have Java in this PC so I can't try it)

I was crazy enough to *upgrade* from Vista to Win7. Almost everything worked, just had to install the latest wireless drivers. Chrome doesn't work. Who. Cares. Anyway. 7 beta is fast and really worht the upgrade. And the taskbar has progressbars when copying or downloading (w/ IE) files. So cute :)