If you are expericing network connectivity fails when you try to use Windows Vista behind a firewall.

If you are facing with slow responds and crashing while your using programs below.

Microsoft Outlook
Windows Mail
Web browser
Remote Desktop Connection (RDC)

I suggest you yo try this steps.

1) Open Command Prompt. (Cmd)
2) Type netsh interface tcp set global autotuninglevel=disabled ( Enter)
3) Restart your computer.