This comes from the back of the Yoda figure which describes him (courtesy of Sir Steve's):

Like the swamp planet Dagobah where he lived out his last years, the Jedi Master Yoda was shrouded in mystery. A diminutive green skinned creature Yoda faithfully served the Galactic Republic as one of the 12 members of the Jedi Council. When the Emperor seized control of the galaxy, he ordered the elimination of all Jedi. In his darkest hour, Yoda, the last known Jedi Master, went into a life of hiding on Dagobah. When Luke Skywalker searched out Yoda for Jedi training on the advice of Obi-Wan Kenobi, the Jedi Master had reservations, but he chose to instruct young Skywalker in the ways of the Force.

The picture above, from the Star Wars Insider #34, shows us how Yoda will look in the prequels. Frank Oz will be pulling the strings (and doing the voice) behind Yoda again, although in long distance shots where the character has to move around computer generated models will be used.

Timothy Zahn's novel trilogy tells us that around the time of the Clone Wars a group of Jedi on the planet Bpfassh went bad. These dark Jedi wreaked havoc throughout the Sluis Sector until they came to a certain boggy planet known as Dagobah. The Bpfasshi dark Jedi were never heard from again.

The Essential Guide to Characters gives us a little hint as to what we'll see of Yoda late in the prequels:

When Palpatine ordered the Jedi Knights purged from the galaxy, Yoda went into deeper hiding on Dagobah. Using the Force and the planet's natural defenses, Yoda was able to discourage visitors, even as his students and students' students were slaughtered by Darth Vader and Palpatine's men.

Unnamed Source: Yoda's role in the new film is not as major as you might expect. He has about as much screen time as he did in ESB and ROTJ, not a heck of a lot (9/17/97).

True Fan: True Fan tells us that Yoda may not appear quite as green in the films as he does in that picture at the top of the page, he may have a brownish color to him.

SPOILERS! Highlight the area below to uncover them!

True Fan also told us a while back that we might see Yoda's homeplanet: "I was commenting on how things with Yoda's home planet, meaning Dagobah, looked great when one of the other Art Directors overheard me and asked my 'guide' if I had seen what they were doing with Yoda's home planet...my guide replied 'no' and gave the guy a wierd look like 'shut-up' and then just continued on like nothing was said..."

The Topps Card and Yoda-creatures: There have been a couple of rumors regarding Yoda's species. With the Ain't It Cool News report on the character known as "Pinky" it does seem that there will be other Yoda-creatures in the prequels. If what True Fan told us up there in the spoilers section is true--and True Fan is a reliable source--then we can count on seeing more of Yoda's people in the new films. Yaddle is one of the other such creatures.

Some of the earliest speculation regarding Yoda's people in the prequels evolved around the Topps card pictured above. Rumor had it that George Lucas presonally demanded that Topps cease printing that card because it ran too closely with themes Lucas was going to explore in the new Star Wars trilogy. Obvious, we can't confirm that story, however it does seem that we will find out more about Yoda's kind in the new films.

Charlton Heston: Charlton Heston will not be playing Yoda. Apparently there was a rumor that he would be, because Rick McCallum denied that such a rumor was true. Nobody we've ever talked to had heard that rumor before Rick mentioned it. There was another Heston rumor, about him playing a new Jedi Master, but that was entirely different.