Yes, you can connect to vatsim on Windows 7 using Squawkbox or FSInn.
Yes, you can be both a pilot and an atc on vatsim (but not at the same time!). You will have to go through the training program to be an atc on vatsim.
as its new, it will work for windows 7
Yes, standard mouse does work with Windows 7.
Yes, Dungeons and Dragons Online will work on Windows 7.
Yes - Open Office will work with Windows 7.
Yes, the Warcraft series of RTS games should work fine in Windows 7. The MMORPG World of Warcraft will definitely work in Windows 7.
Windows 7 will work on a recent Mac (See links below).
It will definitely work on windows 9000 but I'm not sure about windows 7
Yes, it works perfect in Windows 7.
Yes it does! I play it on windows 7 :)
Yes, most of them will work.
If it worked on Windows Vista it will work on Windows 7.