Please help me get all of my a/v equipment to play nice with my new hdtv.

Point of clarification: A single yellow cable is composite and the 3 r/g/b cables are component (reverse from what griphus said above). I agree with everything else.

nota bene, by connecting the TV to the stereo using RCA cables (red/white), you're only getting a left/right channel. If you really want the full surround-sound goodness, you'll need to upgrade to a stereo that has a digital input that your TV supports (e.g. TOSLINK) or you'll need to get something like http://sewelldirect.com/Sewell-Digital-to-Analog-51-DTS-Surround-Sound-Decoder-SPDIF-to-RCA.asp that you'll then use to connect to each of the surround inputs on the back of your stereo.

We have a similar setup: a Wii, a Mac Mini, a TiVo HD and a 2003-era 5.1 stereo. All of the various media generators are connected to the TV. You'll want to use HDMI for this. If you absolutely can't, you want to use component (RGB+RW) cables, but you lose digital audio that way. Give the composite (Y+RW) a miss. For the Wii, get http://www.amazon.com/exec/obidos/ASIN/B000JJRV90/metafilter-20/ref=nosim/. For the iPad 2, either get a http://store.apple.com/us/product/MD098ZM/A/apple-digital-av-adapter or an http://www.apple.com/appletv/. For the MacBook, you want a http://store.apple.com/us/product/TY600VC/A/griffin-mini-displayport-to-hdmi-with-audio-dvi. Connect each of these into the TV's HDMI inputs on the back. From there, we have a http://www.amazon.com/exec/obidos/ASIN/B001TH7GSW/metafilter-20/ref=nosim/ from the TV to the stereo. Most modern TVs do digital audio passthrough, so the TV will simply pass the audio on to the stereo, and let the stereo do the decoding. This means that we use the TV to switch between inputs, and adjust the volume on the stereo. Most remotes can support this.

Isn't the point of a Smart TV to use those apps? So you don't have to connect a million different peripherals? Why not try them?

Also, if your Samsung is like mine, you should have two or three HDMI inputs, one or two component inputs, one or two composite inputs, and a composite output for sound. Each input can be selected using the remote, so no need to wire anything more than once unless you get a new toy. And only buy HDMI cables on Monoprice.com or Amazon. They are marked up between 10x and 20x everywhere else.

Update: 1. The stereo receiver simply plugs into the back of the TV using a plain old red/white composite cable, so that's that. 2. The TV itself has Netflix/YouTube apps built-in, so I don't think I'll need Apple TV if; 3. I buy an HDMI cable and the http://store.apple.com/us/product/MD098ZM/A/apple-digital-av-adapter recommended by TheNewWazoo for the iPad. The laptop is a non-issue, because we can play everything from iTunes using the iPad and stream everything else on the TV. 4. As far as the Wii goes, I can either buy the Wii component cable also recommended by TNW, but we'll probably upgrade to a blu-ray player (which will plug into an HDMI port) and just keep the old yellow component video input plugged in for the Wii since picture quality isn't really a big issue for that device (especially since I mostly use it to play games from the '80s). Thanks again, everyone!

If you nabbed an AppleTV, it has an HDMI port. Run the Apple TV via HDMI to the TV, and the TV's audio via optical audio out to the receiver with the box griphus mentioned. Alternatively, a new receiver might not be a terrible idea -- with the fancy new TV, a few hundred on an HDMI-enabled Denon would be my preferred route. It's not necessary, but it wouldn't be a bad "next upgrade".

So http://img0069.popscreencdn.com/131665245_you-are-viewing-a-used-pioneer-vsx-d457-audio-video-.jpg is the back of your receiver. I assume the remote or front panel has options to switch inputs. You can hook the Wii in with just the standard red/white audio patch (male on both ends) cable, and most likely the DVD player as well. However, it looks like the current models of Apple TV only do optical audio, so you'll need to get an optical -> stereo converter. I can't recommend a specific one, but you'll want something like http://www.amazon.com/exec/obidos/ASIN/B005DIRI6I/metafilter-20/ref=nosim/. I have no idea if that is a good price/product or not.

http://en.wikipedia.org/wiki/HDMI#Cables. If the cable was recently made, you're probably fine, but if you find one in a box from who knows when, and things are wonky as hell, try a newer cable (for the $5 listed above).