Seriously though, you may have to do a fair amount of changes. Are you using the standard code? I seem to think that the last time I saw your forum you were using one of Image's...
The font tag doesn't support that measurement type, though CSS does. Either you are going to have to "CSS-ify" the the forum or use one that has been "CSS'd".
BTW, you won't be able to use "strDefaultFontSize" as an attribute in your CSS because its a variable in the ASP code. You'll be able to search for it in the ASP to find where all the changes need to be made though.
I wish I had a better/easier solution for you ....
Are you using Image's forum or the "standard" code?
If you haven't added any MODs you can switch over to the SpeedBallII rendition which is completely CSS'd. It also has the Site Integration Mod already installed ... always a good thing. If you're still using the sub-forum code you'll have to re-enter that (minus the dbs script), but I've already got it running good for SBII.
You won't need to do anything to the DB, and all your posts will cross over (I made the switch some time back, but I ended up having to re-install a bunch of mods and custom tweaks).