You can use a program like Ophcrack
to find or change the password.
You can read a tutorial for this here
Once you gain access to the computer you can try to delete the partition you created. Since you weren't able to complete the installation it may not be recognized as a dynamic volume.
You will need to open Disk Management. The easiest way is to go to Start> Run and type in, or copy and paste diskmgmt.msc
and then press Enter.
Right click on the partition that you added. A menu will open with the option to Delete Partition, if it is grayed out is being recognized as a dynamic volume. If it displays Delete Partition in the menu you can click on it to delete the partition.
There is a way to delete the partition if it is a dynamic volume, but you run the risk of deleting the whole operating system by trying this. I would suggest learning to live with the partition in this case.