I can get it to work in Netscape 6. And according to the specs, this code should work in NS 3.0+
Try this as a test:
<HEAD>
<TITLE>Test Page</TITLE>
</HEAD>
<BODY>
<FORM ACTION="test.cgi">
<TEXTAREA NAME="Text1" ROWS="4" COLS="18" DISABLED="TRUE">Hello World!</TEXTAREA>
</FORM>
</BODY>
I don't have an older version of NS currently to test with, but it could be malformed syntax that prevented it from working for you.
HTH,
Joseph