Override Cache, Caching CSS, images, etc?

[eluser]Buso[/eluser]
Hi there, I have two questions:
- How can I override cache only for members? (logged in users) I need this because when they log in, more options appear on the same pages (same urls), and they won't be able to see them if the pages are cached. Also, it would suck if the first hit was from a member, and every user (members and not members) start seeing the only-members options.
- I keep reading everywhere that I should cache CSS and images, but can't find anywhere how to do this. Any useful links? Direct help is also welcome =D, indeed.

The main point is to optimize my site (Wallpapers, Images, Backgrounds, Desktops), so if there is anything else I should know, please point it out.

Thanks in advance.