Per today's PD:

Cardinals lefthander Mark Mulder could begin a rehab assignment as early as next week, general manager Walt Jocketty confirmed Tuesday. Mulder, who is nearing the end of his 11-month recovery from shoulder surgery, threw a simulated game in Jupiter, Fla., on Monday. Jocketty said Mulder, who turned 30 on Sunday, will throw one more simulated game and could then begin a rehab assignment in the Cardinals' minor-league system.

The Cardinals would not say how many rehab starts Mulder would need before he would be 'MLB ready'.

Depending on what approach the Cardinals take, Mulder took 3 rehab starts last season before the Cardinals returned him to the rotation (with disasterious results).  

I'd imagine if the results are good, he'll go 3 rehab starts.  They have him penciled in to start for the big league club in early September (per the article).

What, if anything, should the Cardinals expect from Mulder?

The most intriguing part of all this is, "Where will the Cardinals be September 1st?".  If they can shave 3 games off the division lead by the end of this month, September could be real fun.

Ankiel, Mulder, Ryan, Skippy all back with the Big League club.  Potentially Chris Perez as well.  Unfortunately for those players, only Mulder would be eligible for the playoffs should the unthinkable happen.