If you till, you should take the time to add a signifigant amount of amendments at the same time. Generally tilling will leave you with large clumps of grass and roots which should be cleaned up before you lay your seed down.
Tilling will also disturb and cause to germinate hundreds if not thousands of dormant weed seeds that you bring to the surface.
Dave
I have a front lawn (only about 60 x 60) which is basically all weeds.
> The soil is fairly poor in some areas with some gravel in places
> where they probably had a bed for something or another years back. Is
> it OK to just till the entire area without actually digging up any of
> the grass before I start? I assume that all of the weeds will remain
> in the soil and I don't know if this is a good thing or something to > avoid.