According to Friendster, you can sign up with them and create your own little community with your freinds, but if that's not what you want and if you would prefer to run a forum yourself, try these links:
phpBB click here
Invision Power Board click here
YabbSE click here
YaBB click here
The first three run using PHP and require MySQL on your web host. The last one runs using Perl and so requires Perl and MySQL support from yuor web host.