I'm connecting to a Windows Vista computer using my Windows 7 computer. I have a swedish keyboard and whenever I press Alt Gr and 4 combined (should result in a $) the active window gets resized. I have no problem when using Alt Gr to write other special characters such as @ (Alt Gr and 2).
Sound like Alt-Gr + 4 is a hotkey used by some utility probably relating to your video driver. Since it only happens to the remote session, I would assume this is installed on the Vista computer rather than the Windows 7.
So, the first place to look is the settings for any utility belong to the video card. Check the tray icons or control panel to see if you can find the utility.
If you can't find which program uses this hotkey, then you can download a free program from http://hkcmdr.anymania.com/ which allows you to see which program has registered hotkeys.
(Note, I have used this program on Windows 7 (64-Bit), but while it works ok, but it looks like it attempts to restart all your active programs in administrative mode in order to detect the hotkeys.)
The Alt-Gr key seems to be handled in a very special way by RDP. This special handling takes some time. Therefore you should wait at least half a second after pressing and holding Alt-Gr before pressing the second key.
Otherwise RDP will execute a different key combination like Win+Up (or something similar) as you have observed.
Another working solution is to use Ctrl + Alt instead of Alt-Gr.