At least for Windows XP, this list is stored in the registry:

My ComputerHKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionExplorerRunMRU

It looks like there are values a through z off of RunMRU, plus (Default) and MRUList. There is string value in MRUList: e.g., “nkvlsawbhczeyoijfugrtdxpmq”, which determines the ordering of MRUList entries.