What is it?
Originally idleproc.dll is a file included with AOL Unfortunately it is also associated with a kind of spyware known as a keylogger.

What does it do?
A Keylogger will create a log file of all keys pressed on the keyboard. It may send this file to a remote machine. Although I have not confirmed this there are roomers that this keylogger is used as part of the Parental controls of AOL so that parents can review what their kids have been doing online.

More info and Removal
Mcaffe has an application available for download called Stinger. It will detect and remove the keylogger along with other malware that might be on your system.