Aesthetically, I have no complaints. Nice safe, generic blue business colors. The decorative graphics aren't the focus of attention (thumbs up!). The little icons used for navigation are nice.
Some design issues:
1) The main menu is redundant on the home page. You've got the same links and icons in horizontal and vertical fashions.
2) Lots of blank space around that ad on 1024 and wider resolutions. I'm wondering what the page would look like if you took out the horizontal menu, then placed the ad banner to the right of the two boxes that say "Last Shout - " and "You are not authorized to view shouts" (when not logged in).
That would make better use of the real estate without impeding too much on 800 pixel wide screens.
3) Too many borders in the center column. Things would look much cleaner if you took out the dotted vertical borders between the columns (darker of the two) and just had one solid border around "Latest news." Then get rid of the rest of the borders inside that.
4) The login form could use wider text boxes. On IE6/Win at 1024 resolution there's plenty more space for the text boxes. I'd also make the dotted border around the text boxes a solid border.
5) Text size not specified in a relative, em, or percentage font size. You've reduced the accessibility of the site quite a bit in Internet Explorer, which won't resize text if it's specified in ANYTHING but em, en, ex, % or a relative term like small, x-small, smaller, large, larger, etc. Some of us like larger text sizes so we don't have to mash our noses against the screen
6) XHTML is good. Table layout is bad. A 52 KB file is huge for the home page.