Compatible Java versions for early Macbook Pro's

I bought my Mac Book Pro in spring of 2006. Its the Macbook Pro 1,1 2 gig 667 MHz15 inch. I am trying to log into an ebay live auctions and its not working. The instructions say to download Java 1.4.1. and then the soundforge plug in. Here are the links they directed me to.

http://www.java.com/en/download/

http://sourceforge.net/projects/javaplugin/

I don't know how to tell what java version may be on my machine now. Have tried typing "java" into spotlight with no results but I think some version is on there.

Also, if I load this version of java will it overwrite an older one, or for that matter could it overwrite a more advanced version? Does it check to see which is most recent or advanced, or could I install two conflicting version?

Thanks for your help.