If you are using Windows 8, alt + tab is blocked by the operating system. There is a way to indicate in the app manifest to allow this, but that opens up uac woes that will result ultimately in a riot by users (already tried this to get around the, 'run as administrator' thing & it wasn't pretty). Strangely enough, I tried this out in the Windows 10 preview and it works fine without the manifest change. To work around this, the VA beta has a way to target processes all the way down to the individual command level. Instead of alt-tabbing repeatedly to get to another app, you can specify which one to bring to the foreground. There are two ways to do this: either from an individual command performing input (as mentioned above) or by using the new, 'perform a windows function' do display/minimize/maximize a particular app.
With that said (for the rest reading on, including Ice Blast), I'm a little bit confused by the api calls that may cause a directx game to wig out. I have found that if you target another process and then come back to your game, there may be screen corruption. My tests have all been with World of Warcraft 64 bit. I did find that if you minimize your game and then 'Restore', the corruption does not appear. I'm using simple api calls to do this and basically just exposing what is available to the user. It may be that the feature is *too* flexible and might result in a support nightmare. If you decide to go this route, I would suggest experimenting with different combinations of display options until you get it doing what you would like it to do.
Hope that helps some!
Gary