Ah, well I always give up right before I find my answer...
Wasn't getting much on google until i found this.
My resulting statement was:
=IIf([CPR_option]="1", DateAdd("m",24,[CPR_Date_Issue]),Iif([CPR_option]="2",DateAdd("m",12,[CPR_Date_Issue]),Null))
And it did what I wanted. :)