Last week I explained how to turn a PC into a home theater monster. But who wants a PC in the living room? A better idea would be something smaller and simpler — a specialized machine whose only job is to download movies and TV shows galore.

Well, Netflix, Vudu, Xbox, Apple and Amazon all offer boxes that do just that. Although some of them offer only standard-definition video, they'll reportedly jump to HD content soon. I got my hands and eyes on all these boxes, assessing the quality of both their user experience and downloads. Hit Continue for a first-hand tour of Set-Top-Box Land.

The recently released Roku box for Netflix is clearly a work in progress. It’s all standard-def (HD coming someday), but saying its quality is even "near DVD" is a stretch. In a word, it’s awful — nearly unwatchable. There’s also the dearth of new movies (although there are 10,000 oldies), and the fact that most video has a 4:3 aspect ratio, even though to box has a 16:9 option.

On the plus side, it’s dumb-easy to set up, letting you tap into an Ethernet connection or Wi-Fi. I also really like the excellent fast-forward controls, letting you skip to parts of the video you haven't even streamed to yet. After a few seconds, the butter-smooth, hitch-free playback resumes. As soon as this baby goes HD, it’ll be worth its $100 price (plus a Netflix membership) — as long as there's content to go with it.

TiVo HD and Series 3 now link up to the Amazon Unbox service, giving you a fair to good selection of videos to download. They show up in your TiVo Now Playing list, ready to watch. Unfortunately, there are no HD choices yet, but the standard-def titles' quality looks pretty good, about like a DVD. Sweetening the deal is an agreement announced today, where Disney movies from CinemaNow will also be available through TiVo later this year, some of which will be in HD.

After going through an annoying setup process, where you must deal with both the TiVo and the Amazon website, your credit-card payment routine is automatic, charging you $3.99 for rentals of current movies, and $14.99 to buy. Older titles are cheaper, but most rentals require you to watch them within a month — and if you start watching, you have 24 hours to finish.

You can’t watch the video immediately, though. It doesn’t even start downloading for four or five minutes, but once it gets sufficient buffer footage after a minute or two (on our fast 14-megabit connection), you can start. Once it's on your TiVo, the process feels like watching anything on a DVR.

Apple TV ($229 for 40GB, $329 for 160GB) offers more than 200 (mostly old) HD movies for rent for $4.99. I chose an HD flick from the modest list, and the slim, aluminum Apple TV machine told me the movie would be ready to play in an hour. However, two minutes later, it surprised me by telling me the movie was ready. Best of all, their 720p picture quality looks damn good — and includes Dolby Digital 5.1-channel sound.

Apple TV is user-friendly, as you’d expect, but there’s no way to skip ahead into parts of the movie you haven’t downloaded yet, as you can do with Netflix. Still, I like the network-smart Apple TV, which links up with iTunes on my PC, letting me play all my songs from there in my home theater. But the thin choice of HD titles leaves me lukewarm.

If you have an Xbox 360, you already have a box next to your TV that can download fair-looking HD movies from the Xbox Live Marketplace. Downloads are quick, with a long HD movie ready to play after a few minutes. The selection is a whole lot better than it was a few short months ago, but it's still sorely lacking in the high-def department.

There’s a weird currency here, called “points,” presumably to get you to forget you’re spending real money. But 500 Microsoft points cost $6.25, and to rent a current HD hit is 480 points. A quick bit of math tells me that means you’ll spend $6.00 to rent a recent HD film. You also have to watch the rental within 24 hours. It’s a good system, but the worst part is dealing with the XBox 360's noisy fan.

Last is Vudu, a $280 box that wins the prize for the best user interface. Vudu’s perfectly ergonomic RF remote (with no need to point it at the Vudu box for it to work) feels like it was formed by squeezing a squishy piece of clay, designed for simplicity. With just five buttons and a scroll wheel, even the dullest of viewers will be an expert in navigation in about five seconds.

Vudu is slowly building up its movie-starved HD repertoire, and I noticed many of the same Oscar winners and oldsters populating its titles list that are also on most of the others. Most HD titles are renting for between $3.99 and $5.99. I wasn’t as impressed with Vudu’s picture quality, however, looking murky compared to Apple TV but a whole lot better than the underwater-like Netflix videos. Worse, the sound seems to be slightly out of sync with the picture, at least when using the separate optical audio output.

There was one disturbing common aspect of all these boxes: They all ensure you get your movies from just one vendor. The walled garden starts feeling like a prison. Not only do the services load their films up with hardware-strength copy protection, the titles offered are overpriced, especially considering that you don’t get boxed discs with cover art and the extra content often included within.

If you don’t want to break the law, nor have a pesky PC cluttering up your living room, these set-tops are works in progress that are getting better all the time. Even so, the best set-top box is still a PC hooked up to a fast Internet connection.

Video Rebel, Part 1: Cable TV, you’re fired! Netflix, you too
Video Rebel, Part 2: Free HD download guide
Video Rebel, Part 3: Kill your cable, get HD for free over the air
Video Rebel, Part 4: How to turn an old PC into a home theater monster
Video Rebel, Part 5: Download mania! Netflix, Apple TV, Xbox, Amazon Unbox and Vudu compared
Video Rebel, Part 6: BitTorrent and the dark side of downloading