Memory usage

[Jay Pound]

I'm testing an index of 30 million pages, it requires 1.5gb of ram to search
using tomcat 5, I plan on having an index with multiple billion pages, but
if this is to scale then even with 16GB of ram I wont be able to have an
index larger than 320million pages? how can I distribute the memory
requirements across multiple machines, or is there another servlet program
(like resin) that will require less memory to operate, has anyone else run
into this?
Thanks,
-Jay Pound