Hi Glenda,
The other memory slot is located under the battery cover.
Yes, the squared-off area near the battery.

So what I have done is to get the largest and fastest memory card and put it in there.
While the more accessible slot, I used another card and sometimes swap my digital camera's card in there to do a quick viewing of pictures.
Both card slots are the same, they take SD/ MMC and if you got the latest firmware update it can take up the new SDHC cards (up to 8gb per card).
Hope that helps!
You can check out my blog, I do highlight some of the new happenings for the n800. It's
http://1976th.com/?cat=7 for the n800 stuff.
Cheers!