Hi guys... I last looked at this thread back in 2007 and just spent a while trying to catch up. I'll try to summarize for those of you just stumbling upon this thread (or back to it). Hopefully this will help somebody.
There was an FTP server a while back hosting several CDs, but it's long since gone. It was later replaced with a web site that is now also gone. It looks like it's no use posting asking someone to PM or email server info.
People are now posting files on megaupload, which I think is a pretty good idea.
ZGadson posted great instructions a few pages back that explain how to upload a file to megaupload and post the link back here.
Here are the files that have been put up on megaupload so far:
MCA1 v5.0
http://www.megaupload.com/?d=MET7SY3L (thanks ichabodwood!)
MCA1 v5.3
http://www.megaupload.com/?d=5BPNVKRC (thanks BoostTed!)
MCA1 v5.5
http://www.megaupload.com/?d=3KDBWB8A (thanks BoostTed!)
MCA3 v5.5
http://www.megaupload.com/?d=613BOPHH (thanks aurora40!)
MCA6 v5.5
http://www.megaupload.com/?d=2EOXWSFW(thanks aurora40!)
MCA8 v5.1
http://www.megaupload.com/?d=SZHD79EY (thanks KiNgJaMEs!)
MCA9 v5.0
http://www.megaupload.com/?d=NR4MMRVQ (thanks n3d1m!)
MCA9 v5.5
http://www.megaupload.com/?d=KGTX6P9C (thanks ZGadson!)
I haven't tested any of these yet. I'll try to edit this post when I do, or hear of anyone else trying one.
v5.5 is the latest version available for CD-based units, and probably will be the last. v5.5 map CDs require you to update your navigation unit with a v5.5 program CD. There are versions for Nissan and Infiniti. Presumably the only difference is the logo shown at boot up, though I haven't heard of anyone flashing an Infiniti update to a Nissan or vice versa. No one has posted the program CD on megaupload yet. Hopefully someone will, since a few people (myself included) are looking for it. (HINT, HINT

)
If you've got any others to share, especially v5.5 program update CDs or other v5.5 MCAs that are missing, please do!