I just want to reiterate the above. I would avoid graphics if possible. If they are img src that means an http request for each img. I've seen many apply bg images via CSS and then style the text further with a CSS Font Stack. The year is 2009 and we've come a long way with presentation and style. Take advantage of it if you can.
I'm still not convinced that IR or any other CSS hiding techniques are proper use in this scenario. I know, there are plenty of experts in this area and what I state above goes against the grain. So, you may want to utilize that image replacement technique or, if you want, you can invest about 100 hours of required reading here...
User Agent Accessibility Guidelines Working Group Charter
Please don't share all that you find with too many people. Let's keep this on the down low for now okay? ;)