Hey,
The forum's been a little off-size since it was moved to a new setup (a few years ago), but today, I noticed it was REALLY squeezed in. Like posts only scaling to about half the screen width. This makes it rather hard to read. I'm using IE8, incidentally. Looks the same in Compatability Mode, too.
I'm including a screenshot to better explain what I mean:
The forum was recently restricted to 960px wide - so it's not supposed to cover your entire screen unless you're on netbook. The screen shot you're showing seems to be even more restricted than that though - the top bar ought to be exactly 960 as well. Make sure to clear your cache so you get updated css? Let me know if that doesn't work and I'll see if I can scrounge a copy of IE8 and test it out on that.