I've been using the Atahualpa theme for two weeks or so, and I have a Mac so I hadn't tested in IE yet. A week ago a friend of mine told me that in IE, the text grows with each post... and it's true! The first post is my designated font size, then each post underneath that is a step up from the previous one. By the bottom of the page, it's HUGE!

It seems as though this must be an issue with Atahualpa or my implementation of it; I have messed around inside the options panel but I have not done any direct edits to the files.

To see for yourself, my blog can be found here:
http://www.fluffyland.com/blog

Thanks so much for any help you can give!

I took a look... Very odd behavior. Have you tried disabling plugins to see if one of them is causing this? Have you tried switching to another theme to see if the problem persists. That's where I would start.

The problem is in your kicker ATO->Edit POST/PAGE INFO ITEMS->Kicker.... check them all)
it starts with a <h4> and ends with an </064> - changing the </064> to </h4> fixes the problem

What is happening is the IE sees an <h4>... with an <h4>...with an <h4> and never gets a </h4> so it keeps increasing the size of the font because H4 is defined as 'font-size:1.4em' so the firse is 1.4 of normal, the second is 1.4 of 1.4 of normal, the third is 1.4 of 1.4 of 1.4 of normal etc

All the other browsers are more forgiving (ie smart) and figure this out

Perfect, thank you... I had forgotten to put the "#" in front of the closing h4 tag in the date piece!