weird outlines on images and text

I've been getting a weird white outline on a lot of my image files that I made in illustrator. I found out that png files are working better than gif files in cs4. When saving for web, there's two options of png, the png 8 and 24. For some reason it's being inconsistent with which one is working better. Im working on saving new files for my text info so that I can get rid of anything that has that outline. Im having some problems with fitting things into my tables. I'm wondering if there's a way to add padding in an individual cell or if i just need to re-slice my image?