Not too bad. My first comment is with regard to the left column (navigation, monthly poll, affiliates, validation), the title is centered and the text is aligned left. You need to pick one or the other. Personally, I think you should align everything to the left. It just looks a little wonky the way you have it now. Also, you have too much gray. For your titles in the left column, try making them white, same with the ones on the right side (welcome to fearkiller, news and updates). Just to define that text more. You'll also need to put a footer at the bottom of the page, and of every page, just containing maybe copyright, contact and all rights reserved, whatever you want. Just so that the site has a nice finish to it.
In the forums, the login/register line is aligned left, make it centered so it matches the line after it. Right off the bat, the one thing I dont like about the forums is that you have to be logged in to just look at a thread. Not good. You should have it set (like most forums do) to allow the user to at least see what posts have been made in the forums so they get an idea of whats available to read in your forum. Also, you should have at least 1 thread (announcements) that everyone can read and you should put some info about forum policies and welcome info there. Right now, if I was looking for a forum, I wouldnt join your simply because I dont know whats in it, what to expect and its too closed off. Plus, if you can, try installing one of the phpbb forums, its A LOT easier to manage and look at. Btw, you also have no link on the forum page to go back to the main page, add one.
The guestbook logo is unreadable. The rest is great! Again, a link back to the homepage would be great. Try and have your menu available on every page so that the user can navigate wherever they want from wherever they are. Also, your title tag for the page is just Guestbook, you've had all the other titles as FearKiller.net - Title. Keep it consistent and change the title to FearKiller.net - Guestbook.
The other pages look good, very clean and easy to read. I think you just have slight modifications to make for your site to be really great. Its more of a personal site, so what you have now fits just fine. Dont forget to add your meta content/description tag. Job well done.