Trying to cram the design of your existing web site onto the small screen of a mobile device is usually a losing proposition. While you can do a lot by adjusting the CSS stylesheets (for example, you could remove the unnecessary images, make sidebars narrower, or position them after the main text), the end results still might not be optimal for your visitors.
It’s best if you’re offering mobile device support in order to increase the loyalty of your existing visitors, instead of trying to attract (and overwhelm) new visitors, or improve your search engine rankings. With this decision behind you, you can stop worrying about sidebars, deep navigation, pull-down menus, or complex images, and focus on what loyal visitors value most: as much content as you can fit on their small screens, combined with simple navigation.
You might also decide that your mobile user interface will implement only the bare-bones functionality of your web site (similar to the dilemmas I’ve been describing in my article "Introduction to HIJAX"). For example, the mobile version of my blog doesn’t allow you to enter comments.