I have never heard of "dynamic disk" before this. However, searching on here I found this post, see the last bullet point that has a link. Lenovo ThinkPad x61 Dual Boot Installation Option Missing - #4 by Aravisian
I would seriously backup all your data on the disk in question before considering doing this conversion. I see the linked item has a Warning "BE VERY CAREFUL. A MISTAKE CAN RESULT IN THE LOSS OF ALL DATA ON THE DISK.", so do at your own risk.