Windirstat...impressive! Now I have to figure out what to do with it.

I don't see a way to save the results?
Yeah, with Windirstat, I really only run it "interactively" each time, then ALT-TAB to other apps to clear some space by deleting or burning to DVD, then just "refreshing" (which takes less time than a "new" scan). Just now I tried under the "Report" menu though, with the option to "Send an E-mail to owner", and it opens up the E-mail software that your system has its default send mail set to, and pops up a little "Please check your disk space..." message with a nice sorted text view top to bottom.
Also, I'm sure you saw this option but some people miss it, instead of doing a scan of your entire drive (which is never a bad idea the first time anyway) with Windirstat, you can choose the "folder" option and just pick, say, your Documents & Settings folder. This will let it run faster plus "zoom in" to only the area that concerns you and show you more detail in the colored "bubbles". You can even go a few levels down if that's where you see most of your files are residing (based on the text section at the top half of the screen) and run from there, again to get more detail on the true space hogs. If you don't recognize the filename or extention, you can ask here or just Google it to find out what it does and why it might be growing so large for you.
Not sure why you're seeing duplication amongst the different users. I mean, each account will obviously have specific program, setting and user files which will have the same names as part of the profile. Do you mean
data files are residing more than once? What sorts of files are you seeing duped? You may want to use a true "duplicate remover" like NoClone to scan first and see if the files really are duplicates. Just be careful about not removing stuff that's part of setup for those different accounts.
For the Recycler, sometimes I've found "Emptying" the recycle bin (and make sure you do this for each of the accounts you mention) doesn't always truly remove the files especially if there was a problem partway through and it stopped or they otherwise become locked as "in-use". You could try a fresh reboot, then emptying again. If the bin is empty but the files are still there, carefully review them and make sure they're stuff that you really did want gone, then remove them (i.e. through Windows explorer).