MBA use as keyboard for another computer?

You can absolutely do this. Get your MBA and his PC on the same network. Fire up a VNC server app on his PC. On your MBA, use something like ChickenOfTheVNC or even the ScreenSharing app to log into his machine.

Viola!!!

Can't comment on lag, as that would be highly dependent on your network and other factors.

ft

 

I am pretty sure that you won't be very happy with the VNC solution. It is never as instant as a directly connected keyboard.

I' m running several OS's in our company and connect to them via VNC, its always a pain in the ass. The microsoft remote desktop is the only solution of that kind which is close to direct connected performance.

I am really pissed by the VNC / Apple solution (I never thought that there would be a mcrosoft product superior to an Apple product, however RDC showed me the opposite)

 

Enable RDP on the vista machine and download Remote Desktop Connection for your mac.

I use this method to connect to my windows 7 box in my office from my MBA.

 

synergy

I'm not sure in what context you want to exert control over the second machine. I've used the Microsoft remote desktop connection, or CoRD program to gain desktop control over another machine. Those are good solutions if the machines are physically distant, but if they are physically co-located I've used the Synergy program to set up one machine as the main server and other machines as clients. The Synergy program then allowed me to use the keyboard and mouse on the server machine on any of the client machines. In essence Synergy gave me a virtual work space across all the client machines, and it worked across windows, Mac and Linus boxes. You can get synergy from the synergy-foss.org site while RDC is available from Microsoft and CoRD is available from cord.sourceforge.org