Here is how to *easily* fix your system fonts in OS 2008. No theme editing required. It will not change the sizes but will use a different font.

In your /home/user/.fonts.conf file add:

<match target="pattern" >
<test name="family" qual="any" >
<string>Nokia Sans</string>
</test>
<edit mode="assign" name="family" >
<string>Tahoma</string>
</edit>
</match>

Of course, instead of Tahoma use the font you prefer.