I just wanted to post this here as this took me a day to figure out in the end, I figured my NVIDIA update was the problem at first, but after several driver rollbacks, cleanups and reinstalls, system restores and such I ended up at the Wacom driver. It wasn't a suspect at first as it was working just fine before.
So if you have issues with SI or PS CS4 not starting and crashing when the GUI shows up after installing SI2011, try uninstalling your current Wacom driver to see if things will run again.
Apparently the one that is working before a 2011 install is done, can cripple all installed versions of SI and PS afterwards.
My version of the driver was 614-3, I still have to find a version that will work on all version of SI, I will install and test them today and will report here.
Hope this help someone else as well, because this can be so frustrating
rob