Try the following, but try them in the order posted one at a time. If the first suggestion does resolve the problem, then there is no need to try the next two.
0. Go to Start/Run and type: regsvr32 C:\windows\system32\zipfldr.dll /u and click OK.
1. Disable "Automatically search for network printers and folders?": Folder Options >> View >> "automatically search for network printers and folders".
3. Delete index.dat (it may be corrupted). You can find the file via Documents and Settings/(User)/Application Data/Microsoft/Internet Explorer/UserData/ folder, if it is not found there, search your computer and delete the file then reboot the PC.
I don't think that is right - I have just opened task manager and windows explorer and (not doing much else) my cpu usage was showing 10%, just about all being used by explorer.exe and system idle was showing the balance (i.e 90%).
Rocker, I am sorry I don't have a solution for you, but I think you do have a problem. At least this post bumps you up the list!
Is it a Cube branded PC that you have ? Why I ask is I had a Cube branded PC that also used to have unexplainable high CPU usage, I have read on this forum somewhere that Cube are apparantly known to sometimes send PC's out with out of date Bios and drivers, just a thought in case yours was one of these.