I recently did a little research on ike-scan version 1.8 and posted it to my blog.  ike-scan version 1.8 is included in the BackTrack 2 beta release but the new version of ike-scan, which is strangely enough version 1.9, is a part of BackTrack 2 Final.  You should either update to the new version of BackTrack or recompile your ike-scan version 1.8 if you cannot update.  Check out my post to see why:

http://www.cutawaysecurity.com/blog/archives/125

Please post any questions or comments here and I'll respond.
Go forth and do good things,
Cutaway