Java problems, Mac OSX 10.4

For a couple months now, my java has completely stopped working. I have tried to find the answer numerous times, and the only thing I found was to re-install OS for my mac. I really don't want to go through that.

None of my java applications load any more when they were working perfectly fine a couple of months ago. Is there any way to revert back to the earlier javas/ get it working again, and how I can prevent this from happening again?
My system runs OSX 10.4 (Tiger I believe)

thanks in advance for any help

is there any specific way to re-apply java?

I have tried re-downloading the latest update for version mac OSX 10.4 to no avail

it doesn't give an error. In fact it says 'software was successfully installed', but the problems still persist even when I re-start the computer and browser.

Do you suppose there is a way to delete java and re-install it?
I'm completely stumped

I guess I'm not sure what's 'right' in this case.
When I open up Java under utilities, a folder named J2SE 5.0 holds the Java Preferences.
Under 'Java Version' is listed:
J2SE 1.4.2
J2SE 5.O

J2SE 5.O was originally selected, but I changed it to J2SE 1.4.2 but it didn't seem to make a difference.
I'm guessing there is something else I have to do, but I'm not sure what. Either under the preferences or some other settings I have to manually change.