I think this may be the best way to run Weka having more memory, even though I still ran out of memory...I believe it allocated more. This is what I did:
> java -mx100000000 -oss100000000 -jar weka.jar
Still trying to learn a best approach to this. I think as I ran it I was able to use more memory, but it didn't allocate 100000000K of memory, which is what I requested.