hook on create windows?

Hi

I'm doing a program that add transparency to ICQ in windows 2000

Now it is fully working, but I would like to know is there is a way that would be less CPU consuming.

I'm using a timer to check all the opened windows and then check if it is the ICQ contact list or a message window, and after I apply transparency to the window with its handle.

I think that would be better if I could remove the timer because I don't really need it. I only use it to know if another message window was created.

Is there a way to put a hook on that, so when a new window is created I check if I need to add transparency to it, and this without using a timer?

thank you
Krushstone