Anti-virus: you shouldn't really need one (yet, heh heh), but if you want, check out an app called Clamav (and for KDE it's front-end, Klamav)
Flash player: from Macromedia, of course. surf there and you will find an installer (for browsers: Mozilla has directions for you in their site, basically copy or link, can't remember which, some files from the extracted flash player package to some browser dir)
Java: surf to java.sun.com and grab the java-runtime environment package (often called j2re so you'll find it...Java2RuntimeEnvironment). that should do...again, installing it to browsers depends on the browser, but their websites will have info for you.