More than sticky theads, I was thinking of a dedicated forum section (Install and support?), and the "install & support" tab could open the thread for that game.

This approach is fairly simple to implement, because the tab would be just a link to the dedicated forum thread

That sounds reasonable, to not over complicate things, a forum for every game should be sufficient and e.g. "install&run instructions" or "common errors" could be sticky threads.

Also this feature has to wait until the site moved to a new host.

I have an other idea.

on the Game page, we could have 2-4 tabs.

1 - the actual game page, as it is now.

2 - a "forum" or "support" or "something" tab, on which one could access all the forum threads related to the game

3 - a "install&run instructions" tab, on which a simple guide to installing and some dependency info (divided by distro)
This 3rd tab should be made by us users, maybe with a sandbox model (all members could submit install guides, that would just have to be reviewed by a mod)

4 - this tab I am less sure about. "common install errors & solutions" as suggested before, posting error outputs and known solutions to it, would give the site a good google visibility increase

My idea would be, to write a little text in front of the comment section to describe what the comments are for, e.g. posting questions and solutions...

In the beginning i thought that there are numerous places to ask for help about installing/running a game but at it is now, with already some comments addressing these problems, lgdb.org actually looks like the right place.

One design problem actually needs to be addressed first and it would be helpful if you could comment on that too. The comment section doesn't look like the right place for discussions, a forum thread would be much better cause the readability is greater and every question can have its own thread. Right?