need a few help about Hooking

[escap3]

Hello friends .
today, I thought If I can write a program that uses Hook functions I can learn hooking as well .
well, I think it can be a good idea to write a program to hooking Microsft word.
I want to write a program that whenever I take a Save As from my Document in MS Word, when I save it as "1.Doc" my program uses some Hook functions & save it as "2.Doc" .
unfortunately, I never used Hook Functions but I know what can they do & read some articles about Hooking .
now, I need your help . can you please give me some information about these functions, how to use them, & finally how can I write this program also I want to know which hooking functions should be apply to my program .
if some sample source codes are available it can be good .
thanks .

- escap3