I do use RHEL AS 4.0(FCS). I have noticed that kannada characters get garbled even with latest mozilla firefox. The method I use to see kannada characters was 

1. Use the age old MOZILLA not mozilla firefox - It works fine. However surprisingly when I upgraded RHEL 4.0 from FCS to next release, the problem persisted. Then I started using

2. konqueror browser which also displays kannada characters properly. But a bit slow.

Also the tool Brahmi.jar available here would be handy.

We at sampada community hope that you would overcome your problem and post your next comment in kannada. If you use Brahmi.jar, (and ofcourse adopt the age old copy/paste method), you could type and/or read sampada contents even though you dont have browser that displays the characters properly.