If you're havinf problems connecting to port 25 on Windows Vista, try the following :
1. Try using Telnet from the command prompt.
2. If Telnet is not installed, add it from the Control panel.
3. If you can use telnet but still cannot connect, try Telnetting to port 25 on a different server.
4. If still no success, then there is probably some blocking in progress.
5. Try turning off Windows Firewall, and retry your connection.
6. Check the Applciation event log (via control panel/ admin tools) for any suspicious events. Most likely an antivirus program cas blocked connectivity to prevent spammers.
7. Check your Antivirus settings. Mcafee Antivirus had blocked me in my case.
Hope that helps! :)If so, dont forget to say thanks!