Jorge,
I did installed java several times. But never used besides, the need in netscape to enter (and use) certain sites.
I installed from the sun binaries until recently....
Knoppix, quantian are Debian-based distribution, so you've got the powerfull apt-get tool.
Edit
/etc/apt/source.list
and add at the end:
deb ftp://metalab.unc.edu/pub/linux/deve...own.org/debian woody main non-free

(one single line)

then run :
apt-get update
apt-get install j2sdk1.3
This will install the j2sdk1.3
(the whole lot of java package are available:
apt-cache search j2sdk
and you'll see all the package available)
sorry if I put too much details in the apt-get description...
hope this help
talueguito
raul