Unless you're cheating and playing via an emulator on a PC, the Nintendo Wii can't do high definition. One company, however, claims that by using its new device, it can.
VDIGI reckons that its new VD-W3 upscaler can take a Wii game, perform a little magic on it then display it in full, 1080p fidelity (ie "true" high definition). For the record, in its native state, the Wii can only output in 480p.
This doesn't mean the Wii game itself will be in high definition. It's a "cheat", just like many TV sets and DVD players (including consoles) are able to perform, called "upscaling", where a standard definition signal is processed, then output as a (hopefully) cleaner image.
How well your device is able to upscale is up to, well, the device. Expensive TVs do a great job. So does the PS3. Cheaper DVD players, not so much. Chances are, if you have a HDTV, your set is already trying to upscale your Wii's video signal.
For $75, then, you'd want to hope VDIGI's converter is a damn good one. The screenshots on the company's site, taken using a camera rather than a proper screen capture device, don't look great (definitely not to the standard of the Dolphin emulator), but then for some people with crummy upscalers, it'll still be an improvement.
So, saviour or snake oil? I'd lean towards the latter, but until someone gets a proper look at the thing in action, it'd be a bit harsh to write it off completely.