The Drawing Recovery Manager has been around in AutoCAD LT for a while now, making it pretty easy to get your unsaved work back after a crash. (Although you should still save your drawing often!)
But what LT didn't crash? What if you just clicked "Save Changes" and realized half a second later that you shouldn't have done that? (Happens to me on a fairly regular basis.) The Recovery Manager can't help you here -- there's nothing to recover. You said "save", so it did.
Fortunately, there's a mechanism in place to help you deal with this, and it's located on the "Open and Save" tab of the Options dialog. Under "File Safety Precautions", you'll see a box to "Create backup copy with each save". When you check this box (as I highly recommend that you do), LT essentially renames the old file version to a copy with the extension BAK, then saves the current version with the extension DWG. Now you have three saved revisions of your drawing: the current drawing that you have open, the one you just saved, and the one before that.
So, if you need to retrieve the version of the drawing that existed immediately before the last time you saved, look in Windows Explorer for a file with the same name as your drawing but with the BAK extension. Simply change BAK to DWG, and you're back in business. That's all the converting you need to do -- BAK files are exactly the same as DWG, just with a different extension to mark them as backups instead of active drawing files.
To get this to work, though, you must have the display of file exensions turned on in Windows Explorer. Otherwise you won't be able to change the extension, only the file name, and the conversion won't happen. To set this in XP, open an Explorer window and go to Tools-->Folder Options and then the View tab. Make sure that under Advanced Settings, the box for "Hide extensions for known file types" is not checked.
(I don't have access to Vista right now, but if someone wants to send me the location of this setting there, I'll update the post.)