My H1-B with Change of Status is approved; i am right now F1 CPT, i will be on H1 B from Oct 1st 2008.
1. The previous I-94 i got when i entered the country the last time will be invalidated, right?
2. And the next time i leave USA, i need to submit the I-94 on the H1-B approval notice, right?

Don't worry about the old I-94. it will get expired when once your H1 kicks-off.

When you leave the country you have to give both the old one along with your new one.