I had a similar problem but managed to fix it here's what I found wrong:
1. firewall on windows xp machine (comodo) was blocking my vista IP address I had to allow it.
2. A password needed to be set on both computers i think, as i couldn't get access as a blank admin password wouldn't be accepted.
3. Workgroup has to be the same normally needs a reboot to get things working.
4. make sure your typing in the shared names correctly \\homepc\music etc
try pinging the machines too in the command prompt using IP address to see if its getting any response. eg: ping 192.168.0.1 etc