A buddy wanted to link up to play Advance Wars, but we couldn't get more than 5 minutes into a game without my connection from Nintendo Wifi dropping out. This is the first time I've taken the DS online for anything more than downloading Layton puzzles.
I was sitting ten feet from the router at the time, and have a PC two floors away that goes online wirelessly, so I know the problem isn't signal strength.
Searching the web, the D-Link DI-624 that I have should be fully compatible with the DS. Firmware is up to date. I saw a couple of random forum posts suggesting setting Tx rate to anything from 1-2 to 54. I value the stability of my computer wireless connection far more than getting the DS going, so I don't want to mess around with things too much.