Last I heard, the R300 was to be released in Spring 2002 (that's from March to June, I think). There isn't going to be an R250 (though I don't remember hearing that there was one in the first place).
They may "introduce" them, as stated in the article, but the first Radeon 8500 and GeForce3 Ti500 weren't in the public's hands until well after the introduction. I would be suprised if the new cards were released before a firm release date on Dx9 was given by Microsoft.
ArtX is supposedly designing the R300; they had nothing to do with designing the R200 or R100, but I think they may be responsible for the tweaks in the recent series of leaked Radeon drivers (from the 7189s to the current 9005s on Win9x/Me, and from around the 3271s to the current 6006s for Win2K/XP).
ATi announced the intention to buy ArtX on February 16th, 2000 and completed the aquisition on April 5th 2000. That means they've had almost 21 months working on the R300 so far (the R200 would have already been designed by ATi, I'd guess), if they started working on it at around the time ATi completed the purchase of the company. That's plenty of time to design a graphics core. As for what the R300 will have, another thread was posted somewhere showing the R300 with 8 pipelines of 4 textures each and running with a >300mhz clock speed. Whether that's true or not, we'll know in Spring.