Con,
Thanks for all you help in getting me through this same problem. Been playing around with this and I think I'm starting to understand some of this a little better, or at least I'm noticing more things. After you helped me get rooted and past this same problem of not being able to mount the sd card, I came back after a little while and wanted to download adrynalyne's supah clean and ran into the same problem of not being able to mount the sd card and got the same message as before about the disc being corrupt. My computer once again was identifying my phone as a cd drive instead of a removable storage drive. I followed your suggestion again of rebooting the phone while debugging was on and not only was I able to mount the sd card, but when I opened up the J: drive where my phone was connected there now was a folder on my phone called sd card. So I moved all the downloads there and will soon be running adrynalyne's supah clean. I also took my old 16gb micro sd card, put it in an sd card adapter, put the adapter in the sd card slot on my computer and all my folders and downloads were there. So I'm guessing maybe that means my card was not corrupted, but maybe like you said earlier in this thread this may be a bug in DL09.
For anyone else who runs into this problem of the sd card not mounting, just follow DroidXcon's advice of rebooting in usb debugging mode with the phone connected. It has worked for me every time.