Is it really worth to have on board graphic...(I will buy 7600GT)
In short, no.
A P945 chipset board might be more interesting, since these boards are alot cheaper than 965. They "limit" you to DDR2 667 memory - but performance doesn't differ much between DDR2 667 and DDR2 800 in real world applications.
Additionally P945 is not so overclocking friendly as P965.
If you just want a cheap stable board to run your Core2Duo, a P945 chipset board will be fine.