You can collect rent and screen tenants, but almost nothing else.
I've been to a real estate presentation by The Entrust Group (whom Patrick, above, apparently works for).
It seemed solid, and their fees seemed very reasonable. IIRC it was a flat $250 setup and 100-200/yr? Not percentage based, which is nice.
Definitely read a lot into it because you don't want to get in trouble with the IRS and start paying penalties.
But it doesn't seem to difficult, you just write your real estate offers in the name of your IRA, care of the entrust group (or whatever other custodian), and they write the check at closing from your account. Rent checks go to them. Don't ever mix money.