Since the MSR partition is hidden in the Disk Management picture, the 5th partitions sounds right and should work if you had done the original install yourself. But you seem to have an OEM install with the System and a Recovery Partition on the end.
Two things come to mind. The first, if you change the number of partitions prior to the recovery partition, your Recovery options may no longer be useable. There have been folks that ended up receiving error messages when they tried certain operations, like making a recovery CD/DVD. You might try testing your current configuration to see if they still work even before you try anything else.
Also, the fact it is an OEM install may also present problems to a second install because the system may have protection on the install. I have no experience with an OEM type install, so can't help with that.