How do I get Netscape to auto-complete usernames etc.??

I am running Netscape 7.2 for the Mac (OS X Panther) and I had a question regarding auto complete.

I was wondering if it was possible to set up a situation whereby when I start to input my password or username for various sites - Netscape takes over and completes the word for me.

Obviously some sites come up with this option automatically but some don't and I was hoping you could help me with that.

Thanks.