Try these Seven Forums tutorials,
For the partitions: Partition or Volume - Shrink Partition or Volume - Create New
If these don't work for you, then try the free Partition Wizard
After installing the OS you could go to Disk Management, right click the partition, click Change Drive Letter and Path, then click Remove. with no drive letter it will be hidden.
As Everlong18 mentioned, go to msconfig, boot tab and change the timeout to 5 seconds. With no drive letter the second OS won't boot anyway, just put the timeout to '0' and it will boot straight to the old OS.
Unhide is the reverse of Hide, just assign a letter to the partition.
Now, that being said, why do you want to 'Hide' a second OS?
If it's to restore any missing files, just use a backup image program. You should be using one as part of your Disaster Recovery Plan. Backup your HD at least once a week. If you do have a problem you can restore your OS as it was when you first installed it or how it was last week, usually will take 15 to 20 minutes. No need to install programs or activate Windows 7 again. You can also take any files or folders from the backup image and restore them.
There are several free programs that will do this very well. Macrium Reflect
Paragon offers Drive Backup for free
several times a year, it's a good program if you can catch the deal.