OK, updated Firefox to 3.6 v., loaded Java Console 6.0.18 and enabled the plug-in 'Java Deployment Toolkit 6.01.180.7' in the browser.
Always stays the same problem.
Tried reinstalling anew the Java update (18 v.) from the .exe file downloaded to my desktop..., nothing.
Changed 'MSI' for 'JavaHome' in 'HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment\1.6.0_18 \MSI' (as I found it in the 'regedit.exe' Start command, but nothing changes.
Have used many times the Java Verification Page and it shows always: "Oops! You don't have Java installed or you have a version less than 1.4.2"
Maybe reinstalling the OS...?
(Have found many statements in regedit for Java, many of them in relation to the System).