Definately use fluid (expandable) design, but don't be afraid to have fixed-width elements within that layout - ie, a 600px wide table which is centered to the screen in case the window is viewed full-screen. Leverage the flexibility in this medium by using both fluid & fixed types of design (separately or in concert) as the situation warrants. Try to approach it from the users' perspective.

What's up with Faglork, anyway?Don't get all sensitive!
There is a great benefit in controlling your font sizes with CSS, namely that you eliminate the ability of the user to destroy your layout design by increasing the font size and expanding the fonts' containing elements. Remember that fonts expand ANY AND ALL of their containing elements, regardless of the parameters controlling those elements (or the fonts are cropped in the case of an style="overflow:hidden;" parameter). In any case, I think it's a good idea to keep control over the font size. Do make it big enought to read, though. Even younger viewers can be frustrated by tiny fonts.

Bottom line, don't think you have to commit to one layout style or the other. Just do what works.