rdesktop
I use this internally on my network to monitor apps that stay running on my windows server
basically
enable remote desktop on your windows box
install rdesktop on you linux box
point to windows box
done
this is assuming of course that you have everything on your office network configured to allow remote access from outside the network
--EDIT--
you won't be able to tunnel thru ssh this way
so you may also want to check out
TightVNC they have a windows VNC server (I've never tested this option only used the viewer)