I see most of the supported encryption,hash,auth alogorithems on the Watchdog. Please let me know what combination you want to try and we can let you know how to check that on the netscreen.
Or please check 'get config | in <phase one name> and 'get config | in <phase two name>' in the Netscreen to check current algorithems on the netscreen. Now, configure the same on the Watchgaurd.
Thanks,
Vikas