Trouble installing JRE

Hello,

I have ubuntu installed on my machine and eclipse.
I need to install jre also (as one of the pre-req)
I downloaded from java.sun and tried installing this but have been unsuccessful
my machine is old (100gb HD space, less than 1 gig of ram and my processor is 1ghz)
is there an old version i should be downloading?

btw, how can I view my hardware specs on my machine?