@hsrob: 480i? Are you insane? Buy an official Nintendo Component Cable and play your games in 480p and 16:9 widescreen. Then Wii games look awesome, much better than on an SDTV.

Simple answer: You can buy a video component that has a scaling feature, but don't expect these to run cheap.

That failing you can buy a TV with a good internal scaling device but it may cause lag in gaming which may prove detrimental to time sensitive games.
The external scaling components tend to be much better than the ones on your HDTV. With newer end systems like N64 a very good scaler might save it with old stuff like NES It'll help but it might still look pixelated or stretched. A -good- external scaler also tends to run in the neighborhood of 2,000 US dollars.

 It does upscale them...

my ps1 and snes look like crap on my tv ( pioneer kuro) but i don't play them much. all eyes on ps3.

I find it strange, that for people the older systems don't look good on HDTV a lot. All my older systems have looked much better on both HDTVs I've had. ::shrug::

My Wii looks wonderful on my HDTV.  I just use the component cables and have my Wii on widescreen and HDTV in the settings.

Definitely. Well, I wouldn't go so far as to say "wonderful," since I'm spoiled by now on 720p-native Xbox 360 games, but it does look really good.

One thing I might suggest is that, if your Wii still looks pixellated and jaggy after upgrading to component, you're probably too close to the TV. Try sitting a little further back.

I'm 'spoiled' with my Xbox 360 as well. I still find that the Wii looks wonderful on my HDTV.

It's still a 480p signal. The only way it will ever look as sharp as a 1080p native source is if you have the component Wii signal running in PiP mode in the corner. It's still 1/6 the resolution no matter how you upscale it.

For older systems, it is possible to get good, sharp, pixel for pixel output through a computer based capture board system similar to those used for screen captures for print publications.

The real limitation is the output cables for most older systems. The real old ones only have coaxial output (tough to even find a capture board with a coaxial input), SNES era consoles had RCA output with premium cables of the time outputting an S-Video signal. Most capture cards have S-Video input, which provides a pretty clean signal. Component output didn't commonly exist until the 6th Gen of consoles.

It really depends on whether you prefer the look of a native resolution (sharp, but pixelated due to the limits of the source resolution) or an "upscaled" image that is simply composed of interpolated data not generated from the original native source.