Looks like your troubles aren't completely over, though. What REALLY happened?

I noticed a similar problem, about the same time. I had just installed
a Lexmark printer, and was blaming it on them. (Tech Support, bless their evil
little hearts, put up with a lot of abuse, most of it un-earned.)

With an XP machine and a Vista machine networked, I was suddenly unable to
see one
machine on the other. Vista's "Network" and "Network and Sharing Center"
can't
discover the XP machine, although the default network printer (on the XP
machine)
works fine while printing files from the Vista machine.

I tried all sorts of combinations of firewall/none, password/none, private
vs.
public net, and made no progress. I then fired up a third machine (so: one
Vista,
two XP machines). Suddeny, I have no problem accessing files on either of the
first two machines, but the third (XP) machine can't be accessed. All of them
show on XP's Windows Explorer as well as the Vista's "Network" and "Full Map"
off the "Network and Sharing" displays, but the third machine (2nd XP) can't
be
accessed. Message is still "///is not accessible. You might not have
permission..."

Is there something that changed in the latest update that has a counter
one too low, or a pointer one position off?