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You can't upgrade to IE 6 on a Mac...the last official release was 5.2.3 for OS X and 5.1.7 for OS 9.
Try using Netscape 7.0.2 in OS 9. Much more stable and faster than IE in OS 9.
A big boost would be to max the RAM to 1GB. If they didn't like OS X on that Mac because of slowness, it's due to only having 256MB of RAM.
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