Keeper rules are as follows:
1.  Each owner keeps anywhere from 6 to 10 players from his roster.
2.  You will use a pick in the league draft to take your keepers. 
3.  The round where each player must be taken is listed in the attached
 spreadsheet and is based on their prior year draft position.  Each 
 player moves up one round each year, with a minimum of round #15.
4.  You cannot keep two players with the same round unless you either:
    a.  trade for an extra pick in that round, or
    b.  move one of the players up a round
5.  A list of keeper players must be submitted to an impartial
party to-be-named-later by a to-be-determined date prior to the draft. 
This way everyone will know who the keepers are at the same time,
preventing unfair advantages.

So, using my team and Jeff's team (Fenway) in the following example:
Say, I choose to keep A-Rod, he's rated a 1st rounder.  That means in 
the Yahoo draft my first pick MUST be A-Rod, regardless or when my 
pick is in the first round, and A-Rod is a protected keeper for me.  
No one, even if he has a higher first round pick than me, is allowed 
to take A-Rod.  Jeff has two players rated #1, Richie Sexson and Carl 
Pavano.  Say he chooses to keep Sexson, and turns Pavano loose.  His 
first round pick MUST be Sexson.  And so forth.

Say, Jeff chooses not to keep any player rated #2.  In the second
round he is now free to choose any available player (not a protected
 keeper), including re-drafting Carl Pavano.

We use an AL-only player pool.  If you have a player on your roster
who moves to the NL, you must release that player; he cannot
accumulate stats in the NL.  If the player is TRADED to the NL, you
will have first rights to the player coming over to the AL team in the
deal.  In the case of multi-player deals with two or more fantasy 
teams involved, some logic may have to be applied by the commissioner 
(or surrogate) to determine an equitable solution.  The first choice 
is these cases is usually a mutually agreeable deal between the 
affected fantasy owners.

Draft picks are legal tender to trade.  Players may be rented (traded to
a contender and then returned in the offseason) provided reasonable 
compensation is given.