I also wanted to remove all files relating to the above and was stuck with the PIHook.dll file. I could not find where to stop this process so I could delete the file. I worked out a solution and thought I would post it here to close this thread.

By the way, I only had the PIHook.dll file to delete. If you have other files that won't delete, I can't guarantee this will work.

Click Start>Run, type regedit, click OK
Select My Computer
Click File>Export, give a file name and save somewhere you can remember //this will back up your entire registry if something goes wrong
Click Edit>Find, type pihook, click Find Next
//This search sould find the line that loads pihook into the shell
//This may be hard to explain, but here goes
//You should see in the left hand panel a folder called InprocServer32.
Right click that folder, click delete, click Yes
//If you now have a folder in the left panel that has a name full of numbers and letters and has one line on the right panel that has a Data value something like PI5 Ŀ¼¹³, then right click the folder in the left panel, click delete, click Yes
//If you don't know what you are doing, don't mess with anything else in here.
Close Registry Editor
Restart Computer
//I was actually surprised that my computer started up quicker after that
Now you should be able to delete the ArcSoft folder and it's content.

//Should something go wrong as mentined before, Import your saved Registry to put things back to the way it was before, then delete the saved registry file
//Should things be just fine, delete the saved registry file

Hope this helps,
James