I am new to the N800, I just loaded up a card with about 200 songs and put it in th card slot. When I turn on the media player, it just refreshes until I close it. I can play one song at a time, but it wont show me all the music on my card via the media library. The music is all visible wen I look under file management though.

So, how do I get the device to list all my music in the library settings and play more than one song at a time?

My understanding is that the library is updated by a background process called "metalayer-crawler". It is supposed to continually scan and rescan your home directory and media cards for available music and videos. Many users here, including myself, don't like the metalayer-crawler process running all the time and eating up valuable battery time. Thus we disable that process by renaming "/usr/bin/metalayer-crawler" to something like "/usr/bin/metalayer-crawler.off".

Now, assuming that you haven't disabled the metalayer-crawler, you "simply" have to wait a while for your library to be updated. Since I disabled it, my library is never updated and thus I have found the following to work to play a single CD of music.

I organize my music by directories like "/media/mmc1/Yello/1987-One Second/01-Track.mp3". You can load an entire directory of songs into the Media Player, but it is a bit tricky. Open Media Player and then select "Clip->Open...". Navigate to the album directory in the left panel. The right panel will show all the tracks in that directory. SINGLE-tap on the 2nd track. Then TAP-HOLD on the 1st track and QUICKLY DRAG down the list of files until all tracks are selected. Then click the "Select" button. Presto! All tracks appear in the 'Now Playing' list.

I havent disabled anything, but it sure seems silly how long its taking. So, I have deleted all my music off and now am going to see about upgrading or re-installing the OS. I got the tablet on ebay and it probably wouldnt hurt anyhow...

To supplement other replies, I transfer my music to my internal 8G HCSD card directly through the tablet's USB hookup, an album-folder at a time. I have about 200 tracks on that card so far and neither the media player nor Canola have had a problem.
Are you running the 2007 OS, or have you flashed to 2008? It seems to me to work better, but I only ran 2007 long enough to reflash it.