Might help to say a little what your system consists of ... cpu, ram, graphics card etc. I am using win 7 on an ancient 1Ghz Amd, with 1Gb ram and an NVidia GeForce 5200 Agp video card. One problem which I've narrowed down to the video card is that the game BeJeweled 2 Dlx would lock up the system.
With Win 7 on a laptop that has a 1.6Ghz Amd, 512 ram and Via S3G video ... everything runs fine.