cross browser testing

Hi,

what do you do for testing your websites for cross-browser compatiblity?
I have IE6, Opera5, and Foxfire1 installed (in WinXP Pro). What other
browser should I test against?
I tried to find IE5.5 on www.microsoft.com and msdn.microsoft.com but not
there, also tried a google search.
Is netscape even worth bothering with these days? (versions?)

tia

linoj