ATIMMC.exe is a executable that runs in the background so that your TV tuner works. You can end that process but then you'd have to run it everytime you want to watch TV.
What operating system are you running??? How long have you had your OS installed for???
If you are running WinXP, you can check in the task manager to see how much memory each process is using. Maybe that'll help you track down what's causing the problem.
Another possibility is that you are running low on hard drive space and the OS is struggling to allocate space for your virtual memory. Your HD could be fragmented and it's taking a long time for the computer to access certain files.
There could be many many possibilities ... so if the problem is persistent I would suggest just to do a reinstall.
"Sic Parvis Magna"
FKA Silver_SpecV