I tried to decipher your post to see what could be the problem. I had a hard time imagining the network.
So the macbook does work with this setup:
Macbook -> N router -> GBswitch -> WHS
But vista does not work with this setup:
Vista -> G router -> GBSwitch -> WHS
My conclusion:
Linksys G Router is the one causing the trouble.
There have been more posts about trouble with wireless routers broadcasting firefly over the network.
Too bad I don’t know anything about it, but I read a few times about multicast being an option that caused trouble.
Hope I got you on the right track
Kind regards, Erik