How To Temp Vars Or File In Javascript For Other Pages?

We are downloading a few thousand rows of data for users to choose from
and need to speed up the operation. The data is related in four levels.
The current design allows the user to select the first level from about
20 choices and then the next level's choices are retrieved from the
server. This is taking about 4 seconds. We are required to make it
faster.

We need to be able to download all the data once and save it for use
any time this particular page is visited. The app is a support app and
the page will be used throughout the day. The obvious idea is to cache
it in a Java applet but we are not allowed to use applets. The other
idea is to embed it in JavaScript arrays but we have tried this and the
performance penalty is about the same and will be incurred on other
lookups on the page becuase the page reloads for these other lookups
(we are using WebLogic netui).

What we need is a cookie that is not submitted unless the page
explicitly sends it; that is, some data needs to be downloaded once per
session and remain in the browser memory/on the disk throughout the
session. It would be nice if we could write to a temp file or access a
heap - can we? Any ideas?