Is it possible to assign a lead to more than one person?

I would like to assign imported leads to a group of pre-sales engineers who look at imported leads on a first come first served basis - the rep that first calls the lead can choose to "own" it or leave it alone. If they leave it alone, another rep can claim it. So:

1) when I import leads - how do I make sure all users can see all leads and

2) after a user claims a lead, can others see the entry but not be able to modify it - i.e. the entire record is read only.

Thanks,