Thanks for the replies.

tubedogg, I'm trying to do what you suggested:

1) in phpinclude template, I've added the following lines:
include("myhacklib.inc"); // my custom codes
$myvar = myfunction(.....);

2) Added $myvar into the desired template and everything gets parsed and displayed as desired.

What I'm concerned about is whether there'll be any performance issues involved cos the stuff in "phpinclude" template is probably applied to all pages in the BB. So if I've functions that I only require in say, the BB home page, is there any other place I can place it and still get the same results?