As I had mentioned earlier, I bought a hi-definition VGA transcoder box, so that I could effectively gain the ability to view true HD signals on my computer monitor without actually having to dump $500 on an HDTV. At the moment I only have 480p-capable hardware, but for $50 I'd say it was a good investment to be able to do 720p and 1080i in the future.
I took a gamble and bought a no-name "Hi-BOX" off eBay for a couple of reasons. The Hi-BOX was $15 cheaper than Neoya's X2VGA 2.0 and Vdigi's VD-Z3. The X2VGA simply doubles 480i's sync frequencies, meaning that only half a 480i signal appears on the screen at a time, while the VD-Z3 simply ditches 480i altogether. The Hi-BOX, meanwhile, has both a scan converter and a deinterlacer onboard, so it can help out even with older hardware that can't output 480p or higher. Plus, it comes with composite-to-3.5mm audio conversion jacks, which saved me a $5 trip to Radio Shack.
When I first unwrapped the box and plugged it in, the signal quality was pretty disappointing. I'd hooked it up to an old Samsung monitor I have, and even with brightness and contrast set as high as they'd go, the picture was still too dark to view. On top of that, even 480p signals were blurrier than 480i had been on my old TV. I later found that the Samsung monitor was to blame for the brightness problem: I hooked it up to my Sony Trinitron, and the box's defaults turned out to be pretty good. I've got the Samsung hooked up to the KVM instead, since I use the machines attached to that mainly for console work anyway.
After searching through the box's menus, I found that the signal was being scaled up to 1024x768, which accounted for the blurry picture. After scaling back to the proper 640x480, 480p looked amazing on just about everything I could throw at it. The scaling feature on the Hi-BOX is designed for LCD monitors, so that the signal can be scaled up to the LCD's proper resolution. Since CRTs don't have a fixed resolution, I don't have to scale the signal... While I'm on this topic, I still don't understand why we adopted fixed-pixel technologies for HDTV when multiple resolutions were standardized for it.
The Hi-BOX only has component (Y/Pb/Pr) inputs, so theoretically it shouldn't be able to handle composite or S-video signals properly. Remembering back to the NTSC specification, a channel is 6MHz wide, and the Y channel is roughly 5MHz of that. Due to this design it's possible for black-and-white NTSC TVs to display newer color signals in black-and-white, so I decided to hook up the composite line off my capture card to the Y channel on the box. Surely enough, I got a steady signal in black-and-white. Adding color would somehow involve breaking the signal up into Y and its respective two color streams, Pb and Pr, which I'm not going to bother with: the Hi-BOX has a VGA pass-through that I can hook my laptop up with, so I can just pass color signals to my laptop via Firewire and then back to the box over the VGA pass-through using VLC. Complicated, maybe, but it works.
In terms of picture quality, the Hi-BOX's HD support is pretty awesome. Even running in 480i, details pop out much more than they used to on my old TV, and in 480p visuals appear several times sharper and (where applicable) at twice the framerate. The difference between 480i and 480p is subtle on the PlayStation 2, and more noticeable on the Xbox. Surprisingly, for the smallest and generally considered the most underpowered of the three, the GameCube packs an amazing punch in its 480p support - there's a night-and-day difference between 480i and 480p, which almost made me believe that two different sets of textures were used. Consequently, it has roughly the same difficulty rendering at a constant 60fps as the Xbox, while the PS2 keeps up quite well with the higher framerate.
I'm working on a photo gallery of screenshots, which I'll post a link to sometime soon..