>I have another question about the 675. How good is the >internal 4 MHz? Is it as good as a crystal when it is calibrated?

No.

>I mean how stable and accurate is it?

Not very. It's fine for a lot of things, but I wouldn't even consider it for serial communications or RTC functions or the like.

>I need it to an extremly timing accurate project, where i earlier >have used a 16F84 and a 4MHz crystal.

The easy answer here is to use a crystal for this project too.

-Denny