Vitas, it sounds like you just need to give your users access to your gforum login on your home page, no? The easiest way to do this would be to navigate to the gforum login page and copy the source code for the login form and then place that on your home page. However, I think this will redirect your users into gforum after signing in, which you may not want. I'm not sure how you can specify that they return to your home page after signing in. Perhaps if you change the hidden "url" input tag to the target you want?
Michael Coyne
seaturtle.org