I'm not too worried about not having a backup of the videos as I have the original DVDs, I also have another backup of my music.
Sorry I don't understand that.
You can simply treat the Time Capsule hard drive as a hard drive. The backup file will show up as anyone of your files. There is no need to separate the drive out into sections called "partitions". See my screenshot.
But the OP might want to limit the amount of data backing up and make sure he has a certain amount left for his video. In this case, partitioning is required.
Buy a cheap USB drive, connect it to the Time Capsule and keep your music and videos in it. This way you'll be able to include your media files to your Time Machine backups.
I understand the logic. However, I am not sure of a way to partition an AirPort Time Capsule's internal drive. Normally, I'd run a USB drive off the back of the Time Capsule for storage purposes. Please explain if you know how as I am sure it would benefit many!