Create Unallocated Unformatted free space on the C drive[Control Panel> Administrative Tools>Computer Management>Disk Manager>right click the C drive>Shrink Volume]I believe the suggested space for a full Ubuntu install is 16 Gig, I made 41,000 MB about 40 Gig. Just type the size into the already selected box. The wording MS uses is confusing be assured typing 41000 will make 40Gig free space. click next if it asks to format DON'T Also Do Not assign a letter to the newly made volume.