Yes! You need the Wifi Desmume I posted in the suggestions forum the other day (I was requesting it get added to the site). If you have the proper bios files and firmware (which I also posted in the thread) then you can connect to Nintendo Wi-Fi Connection. I think you need to run the emulator as administrator, and you need WinPCap installed. From there it works the same as on a real DS. You do a Game Sync in either Black or White, then do it in Black 2 or White 2. The games will be linked and you can use the Unova Link menu option in BW2 to access Memory Link.
http://www.epforums.org/showthread.p...3-Desmume-Wifi
It can't be done on No$GBA because it doesn't support wifi.
Memory Link is extra cutscenes by the way, not missions. The Funfest Missions you access through Entralink, so far I've only been able to do them solo - I think because it uses wireless rather than Global Link.