Check http://blogs.technet.com/rrasblog/archive/2005/12/22/416421.aspx for information to enable RAS logs on the earlier Windows Versions.

RAS Trace logs help in troubleshooting RAS connections related issues. On the earlier versions of Windows, "netsh ras set tracing * enabled" command enables the tracing. Though this command continues to work on Vista/Longhorn Server, a better place to enable tracing  is from "netsh ras diagnostics".

• To enable RAS logging, run the command "netsh ras diagnostics set rastracing * enabled"
• Now run the scenario that is failing (eg., establish the VPN connection that was failing earlier)
• Flush the RAS logs by executing the command "netsh ras diagnostics set rastracing * disabled"
• The trace logs are created and available at %windir%\tracing folder.
• Some of the trace log files that would help in diagnosing the problem are:
• PPP.log
• RASMAN.log
• IASHLPR.log
• RASIPCP.log
• RASIPV6CP.log
• You can also check the "Event Viewer" under "Windows Logs"->System and look for events with Source as "RemoteAccess" or "Rasman" that could help in troubleshooting the issue.
• RAS Error codes are listed at http://support.microsoft.com/kb/q163111/