I also want to know how to config both portal and gateway, when i tried to execute the perftune, it have error, and then message is "Cannot proceed. Cannot find package sun-portal-core.". My portal are using gateway as http-tunneling for all internal application, the portal cannot be connect when the no. of concurrent user > 500, does anyone have solution about it.
For the perftune script, I had to edit /opt/SUNWportal/bin/pstune-env to change some path. You may also have to edit /opt/SUNWam/bin/amtune/amtune-env, depending on the webserver/application server you use for access manager.
From the error you got, you don't have the same OS and/or portal version. It may be different for you.
About the concurrent user limit, you should also check on psconsole for "Secure Remote Access -> Profiles -> default: Performance Tab".