If you try to install in non expert mode 2 problems : 1. If you already have a dos >32M partition redhat would reside in ext. partition and thus could only be accessed through MBR (which migth be changed by other o.s. installation proccess). 2. If you don't have a dos partition and you create it when installing Cartman, it would be created within ext. partition and thus could not be accessed as "C:" from MicroSoft O.S.'s.
This issue has been assigned to a developer for further action.
This is the default behavior of Disk Druid. Fdisk is available in expert mode installations for user who would like to customize their partitions.