Making music and photos available to Apple TV

I have a double story house with the modem upstairs and an Apple TV downstairs. I also have a USB hard drive with an iTunes library and iPhoto library on it. At the moment every time I want to use the libraries I have to plug my USB drive into my MacBook.

I've recently discovered that my modem has a USB port on it, and I can plug my USB hard drive into that. Can I plug my hard drive into that port and make the libraries accessible to both my MacBook and Apple TV?

If possible I don't want to have to keep my MacBook turned on all the time. I.e., it would be nice to just have the USB hard drive plugged into the modem and access my library on the Apple TV without my MacBook being turned on.

In researching this answer I've read a lot about Apple's AirPort Extreme and how it can do something like that. But unless that's my only option I would rather not spend an extra $200 if I don't have to.