Windows Vista must have the firewall configured to allow other computers to ping you.
By default it will look as though you have no network connectivity when someone pings you, but really you just need to enable "echo requests".
- To enable this, click the Start button (bottom left of screen), type gpedit.msc in the search box and open gpedit
Click Computer Configuration >Administrative Templates > Network > Network Connections > Windows Firewall
open Windows Firewall: Allow ICMP Exceptions then click Enable. Check "Allow inbound echo request" and uncheck the rest.
You should now be able to send a ping and receive an answer.