If you're willing to go DIY, you can build some speakers yourself for pretty cheap. They're very light, so you can easily mount them into a drywall ceiling and save floor space. They also don't tend to oscillate the bass into the room above. Bass is a little light, but they're good for the value.
For the projector, if you're willing to put in some time and effort you can usually find them at auction for dirt cheap every couple months. (especially in an economic downturn...) Mounting is almost always the tricky part though. And the throw distance (how big the screen gets per foot of distance) is the biggest thing to worry about. Depending on the projector's intended use uh... you can too big real fast. Peruse the manual (find the part number for the projector).
You can get a TV the same way, but projectors are almost always cheaper at auction because they're niche and not in high demand. Just keep looking, they'll show up sooner or later.
Keep in mind, projectors are often high latency. You won't notice it playing movies, but if you're playing COD or especially DDR, oh my god that will suck. Most newer models have a gaming mode to reduce it, but most models don't focus on gaming. ALSO, get a spare bulb for the sucker before you actually need it. If you're buying it used you're already halfway through the bulb as is. (unless it's a laser)
White sheet will work fine for a back drop. Official screens will increase contrast but if you have a dark room, not as necessary.
Source: I am literally typing this on a projector. Have been using a PC on a giant projector screen for 7 years now. AMA