You need to go to start->all programs->accessories->command prompt and then type in "sfc /scannow" (without quotes). Windows then proceed to restore or repair any missing or damaged Windows files, like rundll32.exe. If that doesn't work, pop in a Windows 7 installation disk and go to the "repair my computer" section. Let it check your computer and it should fix any missing files.
my pc says I must be an adminstrator to use sfc/scannow, and I can not find my disk for vista. I had them copied when I bought it but I have no idea which one it is on I looked at each one and I do not see vista or the dill 32 it says on the front HP Disaster Recovery Folder