Hello and welcome to the forum. Windows 8 Consumer Preview I don't believe can be installed on a Dynamic Disk. Without any information on the Computer (system specs) and with no information regarding your current disk configuration (disk management) our ability to help is limited. Depending on your physical options installing a second drive (basic disk) to host the Windows 8 Consumer Preview would likely be one of your better options at this point. However you decide to proceed I would strongly suggested backing up your current state by imaging your PC. Reverting a dynamic disk to basic would likely result in everything being lost, unless you have some skills with a hex editor, in which case you might want to read this thread Dynamic Disk Invalid You may want to consider installing the Consumer Preview to a VHD, in which case simply use Google (Install windows 8 cp on vhd) and that might be an option you can employ.
As this is a pre-release version, please be cautious as to how you go about the installation and avoid upgrading your current OS, ideally you may wish to test on a non-production machine, virtual machine, dual boot scenario or a completely separate drive installed alone and used independently for this purpose only.