anyone buying an appletv for HD is going to be bitterly disappointed in my opinion. It can barely manage 720p in its basic form.
from the ipad spec page:
Support for 1024 by 768 pixels with Dock Connector to VGA Adapter; 576p and 480p with Apple Component AV Cable; 576i and 480i with Apple Composite AV Cable
H.264 video up to 720p, 30 frames per second, Main Profile level 3.1 with AAC-LC audio up to 160 Kbps, 48kHz, stereo audio in .m4v, .mp4, and .mov file formats; MPEG-4 video, up to 2.5 Mbps, 640 by 480 pixels, 30 frames per second, Simple Profile with AAC-LC audio up to 160 Kbps, 48kHz, stereo audio in .m4v, .mp4, and .mov file formats; Motion JPEG (M-JPEG) up to 35 Mbps, 1280 by 720 pixels, 30 frames per second, audio in ulaw, PCM stereo audio in .avi file format
admittedly the 720p support sounds like a winner over ipad's 1024x768 but I doubt you'd be able to see the difference. My main point is it's basically a terrible time to buy the stupidly underpowered and outdated appletv, but a great time to buy the bleeding edge ipad.
FYI I own an appletv and have done more or less since launch, I wouldnt however reccomend it to anyone anyore, just too much money for such a weak, outdated and singleminded product.
Sorry - thats just the way it is.