John, a vanilla ATV will not work in the way you want because Apple hard code ATV's to have a local relationship with a Mac running iTunes and a cloud relationship with the iTunes store: You will need to jailbreak your ATV for it be able to see a NAS on your network. XBMC and FireCore have quite devoted followings though I've never attempted this personally.
I ran a TC as a NAS for a while, but the disk speed is too slow for it to be useful as a media server IMO. It will work, and partitioning the drive through Disk Utility (which is in your applications/utilities folder) will allow you to create the partitions you're seeking (photos, music, movies etc). However until you jailbreak your ATV this will essentially be meaningless (since, as mentioned, ATV is designed NOT to be aware of NAS drives).
You are also starting to encounter the walled garden of Apple's design "philosophy": Apple wants you to store your content in iTunes on your Mac, this is why its ridiculously easy to get content on an iphone, or an ipad, or streamed to your hifi through an Airport Express. What you're trying to do is outside the design philosophy of "the average Apple user" and hence the pain curve increases exponentially.
I would strongly recommend returning your TC if you have no desire to use it for your Time Machine Backups: It excels at this function and frankly is only adequate at being a NAS: It sucks as a media server so that money could be better deployed elsewhere in your setup.
I would consider taking a look at a dedicated NAS, Buffalo are good and relatively price sensitive, Qnap would be better since their software now supports the Lion architecture and they have a dedicated iTunes server mode, which means you don't need to have your macbook running to stream music around your house (though not Movies and TV shows - which isnt a problem if you jailbreak your ATV).
Finally, the iLife apps on your Macbbok are all designed to work locally from your Mac, you CAN have remote libraries but again you're now outside the design philosophy of the "average Apple user" (Apple considers running an external photo library a pro requirement, and therefore THAT customer would use the pro photo app, which is Aperture - the net result, iPhoto sucks at managing libraries on a NAS). Check out iPhoto Manager, its around £20 and helps get round this problem.
This is a very long and waffly answer to your question, your next steps IMO should be:
1). Partition your TC thruogh Disk Utility.
2). Create the folders you want in your TC partition (Music / Movies / TV Shows / Photos).
3). Copy your content from your Macbook to the corresponding folder (do NOT delete the content fro yoru macbook).
4). Jailbreak your ATV.
5). Test your ATV to make sure it can see the volumes in your TC NAS.
6). Holding down the option key: Load iPhoto.
7). Select "other library" and navigate to the Photo's volume in your TC NAS.
8). Update the iTunes Media Folder location (preferences/ advanced/ change)
TEST, TEST, TEST and make sure all your photos are there, they sync to your iPhone etc (in fact, do this for all your content).
For safety's sake, I would take a complete backup of all your content, ideally either into the other TC partition, or to an external hard drive and only then, consider deleting the content from your mac.
I hope this helps.