firstly if i upgrade from tiger to snow leopard can i use the $30 disk as i have read. secondly, will ilife '07 and other programs still run properly. finally, is it worth upgrading if im using a first gen macbook core duo with 1.5 ram?
Yes you can upgrade to SL from Tiger, no questions asked - though Apple does recommend you get the Boxed Set.
iLife '07 will run definitely, in fact most applications will run. However, do check with Apple or this wiki to see if your application will run. Just to clarify - SL will never delete your applications, if it is on the blacklist, it will just move it to a folder.
Of course it's worth upgrading - even more so because you are on Tiger. ;)