Max post length

Hi,

I started blogging with WordPress last week. Now i use the fSpring widgets basic skin. Now i would like to make a max length of the post that you see on the main page. and u can see the rest of the post when u klik on the link where u normaly see the comments.
It would be very handy that i know how to do this, because there are 2-3 blog posts every day probably more on busy days. But posts made in the moring whill completely be invissible is there is a big post right above. If any one could help me with it please.