I put a
if(is_home()) bit in my theme's functions.php and it doesn't seem to work. The function containing this bit is called on init so
is_home should work already.
To follow up on John's answer: Add a call to said function on one of the hooks mentioned by John and hakre.
Add, e.g., the following to your functions.php:
EDIT: I misread your question at first -- it looks like you've got a function encapsulating the code already, it's just that you're firing on the wrong hook. Either break that section out into a separate function and have it fire at template_redirect, etc., or change where you're hooking in the first place.