I'm actually running Offsite in 1280x1024 mode and it works fine. The way the fonts work is that there are six total fixed size fonts of which 4 are used depending on the resolution of the PC.
When we've seen this problem in the past, it seemed to have something to do with the video driver. You could try seeing if there is an update for your video driver or a vendor specific driver for whatever card / builtin video hardware you have.
I'm assuming you are actually getting the ICE fonts, not a system font. You can see this by trying to display a page with line graphics, i.e. the scoadmin program or something similar. If you are getting a windows system font instead of the ice fonts (typically Ice4370.fon) you might want to try to reinstall. You may want to check your windows fonts folder to see if you have more that 512 fonts in it. This has caused some people trouble in the past.