If you haven't already solved your Vista problem - you could have a look at this. Am assuming you are talking about wireless connection.
Check that your Vista machine has the same security settings as your router - the IP addresses need to be the same.
Check to see if your wireless network adapter needs updating - go to device manager to do this
Check the TCP/IP protocol settings - look at this article
If IPv6 is checked uncheck it leaving just IPv4 checked.