Well first of all you have to get yourself some RAM, 512MB is not enough for a PowerMac, 2 GB minimum is more like it.
Next you mention you have digital cable.
The problem is this, the US market is slowly changing over to a digital signals but the most channels/broadcasters are still using analog.
Your comcast cable box is digital, but most likely it's passing the analog signals through.
Now comes even more problems.
The EyeTV 500 only processes unencrypted HDTV ClearQAM digital signals (and over the air ATSC), so your only going to get a few "free HD" channels like you would if you set up a antenna.
All the other channels, Showtime, HBO, Cinemax, ESPN and the like in HD format use content protection which requires a HDCP chip in your TV. The EyeTV 500 doesn't have that chip.
Another problem is because a lot of channels are still analog, this requires another device like a EyeTV 200 which only processes analog signals.
The only good thing about this is if you have both the EyeTV 500 and 200, the same EyeTV software will run both, just pops up another window. You can run both at once if you don't have a digital cable box, that I do know. If your Free HD comes clear down the cable like analog is.
So with both the 500/200 you get all the analog stations (hopefully) and the "free HD" stations (just a few) on a Mac. But all the juicy stuff in HD or digital signals with HDCP content protection your going to have to watch on the regular HDTV.
One more problem, if you hook any other device like a three way splitter after the output of the cable box, you might not be able to see the HDCP HDTV programs on your TV. Because the TV and the cable box "talk" to each other to keep the content constantly encrypted. Anything else on the line can interfere with this. A switch might work though.
But anyway your talking a lot of cash to watch TV on a Mac to get little and eventually analog will be phased out, sometime by 2007-2008.
However you can just watch the analog channels with a EyeTV 200 until it's finally phased out.
