A "picture" (e.g. screenshot) of what DISKMGMT.MSC shows for your hard drive would be very helpful.
Depending on the physical layout of the two partitions on your drive, you many need to "move" things around as part of your goal to resize things to add some additional space to your Windows 7 partition.
Note that EACH OS sees itself as located on "C" when it is booted, but sees the other partition as a different drive letter (either D, or E, or you say B... whatever it initially was, or what you changed it to using DISKMGMT.MSC). What we really need to know though is the PHYSICAL layout of things on your hard drive, in order to prescribe an approach to accomplish what you want to accomplish.
I'd suggest you download and install Paritition Wizard (free) Home Edition v5.2
along with its standalone boot CD which you can burn by downloading this ISO file
. The program itself runs under WinXP, Vista and Windows 7, so you can see drive letters (per the installed OS under which you run the program). But mostly, it will present the physical layout of the drive, which is what we need to see. A screenshot from PW would be helpful, although one from DISKMGMT.MSC is fine as well.
The standalone Partition Wizard boot CD is for emergencies, disaster/recovery, and for partition-related operations that cannot be performed while the Windows 7 operating system is active but must be run while standalone booted. It is very possible that you will need to use this standalone boot CD to accomplish the resize/relocate/move for your two partitions, as performing movement of OS partitions is normally not something that can occur while the OS is booted.
Please let us see a screenshot from DISKMGMT.MSC or Partition Wizard, of your hard drive layout.