what you have done is installed linux on a windows partition.
it works, but isn't really recomended for a workable linux installation.
as you have a seperate partition that you want to you for linux, i would recomend reinstalling it on a native linux partition.
you will also have to make a swap partition, 100mb should be fine
then you can make a partion for /, the root directory of linux
then you will be able to choose what to boot from at bootup
if you have any problems or more questions feel free to ask, we should be able to help you with them