Looking through Program Files I find that I have over time accumulated 6 versions of Sun Java ranging from 1.5.0.03 to 1.6.0.10 b33 and taking up 400MB of disk space.

I really don't understand what Sun Java is for (I gather it is for games but I do not use games) but anyway do I really need all 6 versions?

I am told that M$ Java is much better so should I install it and if so how do I get hold of it? (I gather Sun legally forced M$ to discontinue M$ Java.)

I was using Win98SE but was forced to switch to WinXP SP3 when I recently bought a new machine.

The latest version of sun java is not bad and relatively secure.
I would download it from:-
http://www.freedownloadscenter.com/Utilities/Disk_Maintenance_and_Repair_Utilities/HDHacker.html
Before installing go to Add/Remove programs in the Control Panel and uninstall all previous versions and then install the downloaded version. You should be good to go.