I have managed to get the Legend Limiter I used 9.3.1 to work in Arc 10.
Install Legend Limiter as before, you will notice nothing seems to happen.
Then go to:
C:\Program Files\ArcGIS\Desktop10.0\Bin\Categories.exe (Component Category Manager)
In this window click on the button Category Importer...
The LegendLimter.dll should be visible. Check the box and then Apply Changes.
Now you can add the Legend Limiter button in ArcMap from the customize tool.
Hope this helps.