There is a DIRECT pathway
http://www.sirweb.org/gradEdu/DIRECTpathway.shtml
offered here:
University of Florida Health Science Center-Jacksonville
Northwestern Memorial Hospital
Georgetown University Hospital
Brigham & Womens Hospital @ Harvard Medical School
University of New Mexico School of Medicine
And then there is a 'clinical' pathway
http://www.sirweb.org/gradEdu/IRresidency.doc
which is offered here:
Institutions Participating in Clinical Pathway
Dartmouth Hitchcock Medical
Contact: Kevin Dickey, MD at (603) 650-5846
Medical University of South Carolina
Contact: Renan Uflacker, MD at (843) 792-6160
University of Pennsylvania Medical Center
Contact: Mike Soulen, MD at (215) 662-6839
University of Virginia Medical Center
Contact: John F. Angle, MD at (804) 924-9401
More information on the exams you have to take (and their prerequisites) can be found here:
http://www.theabr.org/DRAppAndFeesinFrame.htm
http://www.theabr.org/VIRframe.htm
It is my understanding that for match purposes the 'clinical' pathway positions are treated as PGY-1 positions. The 'DIRECT' pathway positions are open to people who already have 2 years of residency training in a different specialty (typically surgery). So they would be matched as PGY-2 positions (if they will be in the match at all).
Your best bet is to look up the programs that offer either 'DIRECT' or 'clinical' positions and to contact them about the details. This is all pretty new and in flux, so most of it is probably not chiseled in stone yet. There is also some information on how to become an IR on the SIR website:
http://www.sirweb.org/gradEdu/graduateEducations.shtml