There are quite a few sites out there (use a good metasearch
engine like ixquick.com) where you can find the info. Search on
'browser neutral'
There are 'canned' browser neutral javascripts out there for most
of the functions needed.
As far as the other issues, most developers simply ignore them
and code for IE because they own over 90% of the browsers in use.
It can be a lot of extra work to make sites happy for all ( IE,
Netscape, AOL, WebTV, etc.)
The problem hits you when you try to submit a site to Yahoo that
will reject it if there are significant Netscape problems.
Good luck. Either keep it simple or bone up on the differences (
table cell background images, neutral javascripts, et al.)