I have a dir625 d-link wireless n router. The Intel pro abg adapter on the motherboard works great, but does anyone know if there is a 802.11n usb adapter that might work with it. At time my notebook disconnects and I wonder if the 802.11n might stay connected a little better.

Welcome to LQ!

My personal opinion (which may very well be wrong) is that looking for a USB 802.11n adapter has two problems. First, it is USB, which from what I can tell from the threads here, almost always presents more problems than non-USB wireless rigs. Second, 802.11n is still pretty new (and not finally ratified) which means that even Windows drivers are likely to be flaky.

You've got an Intel adapter already, and Intel is actually one of the good guys in Linux wireless. You might consider moving to the absolute latest kernel (2.6.22.x) as starting in 2.6.22, there is a new wireless stack available, and from what I've been reading, Intel has been saving some driver improvements for this new stack. You'd have to compile your own kernel as I doubt that your distro has moved to the new stack, but it might be a good experiment to try. Also, if disconnecting is a real problem, you might have a look in your log files (/var/log/syslog, /var/log/messages and the output of dmesg) and see if the driver is giving any reasons.