As referenced in this thread:
http://forums.contribs.org/index.php?topic=27082.0Which references this howto:
http://www.vanhees.cc/index.php?module=ContentExpress&func=display&ceid=18&meid=Thanks heaps Master Sleepy!
I should note that I had NO success with kernel 2.4.27; both internal & external interfaces on two different machines seemed to be configured correctly but would not communicate. Adapting the instructions slightly for 2.4.26 (also available from the latter page) was simple enough and did result in a noticeable improvement in establishing VPN connections to the server. (No 619 errors at all, so far, on both machines!!!!! From both 2000 and XP SP2!!!!!)