Thats because you put windows on then tried to partition it, which you can't do (well you can with some 3rd party softwares I think). The best thing to do though is partition it before you install windows. When you boot off the windows cd it lets you format and partition, first you should delete any partitions that currently exist (after you have crucial data), then partition them into 2 and format the one to install windows on. Once you are in windows go into computer management and format the other partition to add it as a drive.
And partitions won't have any affect on speed in a single drive scenario, its just for organization.