chiarafumo answered his own question:
I remembered that in:
HKCU\Software\Microsoft\Windows\CurrentVersion\Policies\Explorer
I had created the entry NoDrivesInSendToMenu with a REG_DWORD value of 1. once i set it to 0, the problem went away. [well, so far, anyway.] but in case anyone does a bonehead thing like i did, they'll at least be able to search the forum and discover their mistake.