If I buy Picture It 99, will I be able to use it on Windows 7? Will I be able to open photos with the .mix extension that I am unable to open with any programs at this time?
No, you won't be able to run this application on Windows 7, because it was released a very long time ago and it was developed to run only on Windows 98, Windows 2000, Windows 95. But there is also an alternative to this application. It's called XnView and it's capable of opening MIX files.
Download it here: http://www.xnview.com/en/xnview/#features
I have run this program on WinXP and now run it on Windows 7