delayed appearance/update of index.php

My question is this:

When I modify and save my CSS.php, it immediately changes the appearance of the blog in the browser so I can check bit by bit what I’m doing/wrecking easily.

However, when I modify index.php (the one within the theme’s folder) it takes a good few minutes to appear as changed in the blog.

Is this normal? Meant to be? Nothing to do with wp and something to do with something else? (how vague is THAT!)
I’d just like to know if I can get round it as my php skills aren’t brillo, so I have to do things step by step.
thanks ??

a bit more info….: I started using the Barthelme theme, and barely modified it as I really liked it as it was as i put in a lot of graphics in my posting. But (of course) it fails in IE (I’m on a mac, so didn’t realize for a few days… I suppose it’s the three columns that’s causing it. )

ANYWAY, I just wanted to re-jig it so that the comments/permalink etc are included in the post container until I have more time to dedicate to fixing it.