Here's a section from a thread that addresses the problem:

I had a similar problem. I had installed Office 2007 without problem, and
subsequently applied XP SP3. After the SP3 install, various dialog boxes in
all Office2007 apps behaved weirdly with obvious and ugly font substitutions
taking place, for instance in the text on buttons.

Following the thread here about Arial, I examined my windows Fonts folder
and noted that about 5 other fonts including Tahoma and MS Sans Serif had
been updated in the SP. I removed the new fonts (in Safe Mode, XP does not
permit in normal mode) and used the old files from the
/windows/$NtServicePackUninstall$ folder to replace them.

So far, things seem returned to normal in regard to these fonts bahaviour in
dialog boxes.

Here's the thread.

Most of the immediate chatter has been about Arial black, but Tahoma, Impact and some other fonts are being mentioned, too, as having this problem after the SP3 update. I haven't noticed a problem with Tahoma and don't use Impact, so that problem hasn't turned up.

Here's a link for a quick fix for Arial black, but it does mention Tahoma.

Essentially, you're deleting the new fonts and fetching the old ones from an "uninstall" folder. I can't find the font names on Tahoma, though. You might be able to pick that up in Windows Font Manager. 

Good luck on this.

Owen