There are a number of reasons why the systems won't auto show up in each others finders / discovery windows. So let's put that issue aside.
Open Terminal (spotlight / terminal).
Run the following replacing 192.168.15.10 with the IP of your vista machine:
nmblookup -A 192.168.15.10
You should get a response back similar to the following:
Looking up status of 192.168.15.10
NAS1 <00> - B <ACTIVE>
NAS1 <03> - B <ACTIVE>
NAS1 <20> - B <ACTIVE>
WORKGROUP <00> - <GROUP> B <ACTIVE>
WORKGROUP <1e> - <GROUP> B <ACTIVE>
MAC Address = 00-00-00-00-00-00
If you don't, double check your windows firewall(s).
If you do, try connecting to the windows machine by going to the finder, hit option-K, and inputting the following (again, changing 192.168.15.10 to your vista machines IP).
smb://192.168.15.10/
and selecting connect.
Report back if it doesn't work.
One other thing to try (I see this a LOT on my wife's MacBook), open terminal again and enter:
arp -d -a
Then try pinging the Vista machine again. If it starts pinging, try your connections again.
Michael