I agree with the others that it's your browser's cache, rather than your connection most likely at fault.
Gmail depends entirely on your cache, which is what makes it fast to use.
You might find this helpful, it's google's guide to clearing it:
http://mail.google.com/support/bin/a...topic=0&type=f
Java run time that java.com provides and the javascript in your browser that gmail uses aren't related, so that download won't help, although having the new Java 5 is nice and worth doing.