Can I do hdtv resolution playback in catalyst?

Depends what you mean by hdtv.
There are many different formats.

http://www.dlpstore.com/techguide/hdtv.asp
http://www.projectorpeople.com/tutorials/hdtv.asp
http://www.cybercollege.com/tvp009-2.htm

Most of which require too much hard disc bandwidth to be useable.
This is possible using custom hardware like the Pinnacle cinewave system.
http://www.pinnaclesys.com/
http://www.pinnaclesys.com/displaydo...10&Langue_ID=7
http://www.creativepro.com/hardware/home/1451.html

"But some new technology might make higher resolution Quicktime playback work in the next Mac OSX, v10.3
10.3 will include a new codec, called the Pixlet codec, designed by Pixar and Apple, for doing HDTV playback on desktop macs.
Apple is calling Pixelet 'Studio grade playback'.
Pixlet is the first studio-grade codec for filmmakers. Pixlet provides 20-25:1 compression, allowing a 75MB/sec series of frames to be delivered in a 3MB/sec movie, similar to DV data rates. Or a series of frames that are over 6GB in size can be contained within a 250MB movie. Pixlet lets high-end digital film frames play in real time with any Panther Mac, without investing in costly, proprietary playback hardware."

http://www.apple.com/macosx/panther/
http://homepage.mac.com/macsatin/C12...1/E1509052356/

More info on wavelet compression at
http://faculty.gvsu.edu/aboufade/web/dw.htm