To connect an Apple TV to a projector, you usually need an HDMI to VGA converter. Your best bet is probably this one from DealExtreme.
I'd also recommend a VGA switch so you don't have to keep swapping the VGA cable between your computer and the Apple TV. Some options are this from Amazon, this from DealExtreme, or this from Monoprice. You'll also need a couple of extra VGA cables, which can be found around your school or from one of these online retailers.
VGA splitter to have the same image appear on a monitor and the projector, you can put the VGA switch before that splitter to have the Apple TV image appear on both, or you can put the switch after the splitter to have the Apple TV image appear just on the projector.
You may also want to to be able to have both the Apple TV and a computer hooked up to the same set of speakers. If your speakers don't have two inputs, you can get a headphone splitter such as this one from DealExtreme or this nicer one from Monoprice. You'll also need a male-male 1/8" (3.5mm) cable.
If you're just looking to convert the HDMI video signal to VGA, your cheapest option is probably this one from DealExtreme or this one from Amazon.
If you're using an HDMI to VGA device that doesn't convert the digital audio to analog audio for speakers, you'll need an optical audio to analog audio converter such as item 6884 from Monoprice (or this one from DealExtreme). If you're plugging in regular computer speakers to one of those you'll probably also need something like item 5612 or this from DX.
For iPad cases, my favorite is the Monoprice TPU skin, available in red or smoke. It's also available for the iPad mini in black or clear.
In general, my favorite sites for cables, electronics, and such are Monoprice, DealExtreme, Element14, and of course Amazon.
- Monoprice has high quality items, great organization, good prices, and pretty quick shipping. Unfortunately the shipping is not cheap, and if you order more than about four pounds worth, you will likely get charged import duty at the Canadian border.
- DealExtreme has very cheap prices, and free shipping, but unfortunately the shipping is slow and there are a lot of products to sift through to find ones that might be good for your purposes.
- Element14 has great products that are well organized, but again there are a lot to look through. Unfortunately it's designed more as an electronics components site, so they may not have the cables or electronics that you're looking for. Shipping is very quick and inexpensive, though, and prices are good.