is there a way to let robots doing their job at members only view pages of my forum for having better optimization?

may be its funny question but i had see some php forums to do this, and when you try to folow the link they send you at login page.

I'm not sure I understand the question. Are you trying to keep bots from spidering your members only pages?

If so, you should be able to do that with your robots.txt file. Granted its not fool proof, some bots don't play by the rules, but it should work in most cases.

of course it is possible. basically you grant search engine spiders a "wild card" to spider your members only forum. however, if users have to register and login first to see the actual content, it might be considered cloaking.

You also have to make sure that the spiders are able to spider your "normal" (ie. ?post=242&session=484242&thread=4384) URLs... in most cases they arent. this is why there are "archive" add-ons for most forums which create an archive of all posts of your forum with search engine friendly links.