[mod_python] IE not using cached images

Please excuse me if this question is elementary. I am having trouble
with IE and its refusal to use images it caches. What happens is the
first time I hit my site, everything works as it should - all images are
downloaded, etc. If I then hit another page on my site with the same
images, IE refuses to use the images in its cache and instead requests
all of them again. Not only that, but the rollover images are requested
each and every time I put the mouse over the images. Now, if I hit
reload, then everything works fine again. If I hit another page, again,
the same problem, over and over and over again.

Now I've played with IE's settings and have discovered that setting
"Check for newer version of stored pages" to "Never" makes IE act as it
should. And I have checked if the images are actually getting cached,
they are. I have also tested other browsers (Opera, Netscape, etc.) and
none of these have the same problem.

Now to the question, should I be sending the client something (304?) to
tell it to use its cache unless the user specifically presses reload?

OS: FreeBSD 4.7
Apache: 1.3.27
Mod_python: 2.7.8
Python: 2.2.2

Thanks,

Jason