shouldn't matter too much for you. 120gb hard drive will fill up fast if your recording HDTV, figure roughly one hour = 3+ gbs.
I can recommend a few places where to get good info-one is to research via www.newegg.com

Another thing would be to post in a forum like
Overclockers.com forums
Some guys there can give you excellent advice on best price to performance.

XP Media a good product? Sure, it works fine. You might think of getting Vista though, it was just released two days ago.

Most people say SATA is better than EIDE, I agree.

I have XP Media and record from my DirecTV (not HD) frequently. No problems. I have a 120g hard drive, like apilgrim said, it fills up pretty quickly. I recorded 3 hours of UFC 66... it was about 10g. Most programs aren't a problem to burn to DVDs, though.

They have HD DVR's for DirecTV

Man, gotta have the DVR...I would pick that over the HD if I had to choose.

Core2Duo is the best processor on the market right now, but I am not sure it matters much for you.

Get as much HD space as you can.

SATA is much faster then IDE.

Vista is complete crap. Media Center is a joke in that its basically XP Home but with a fancy new label. Just use XP Pro or whatever you have that you can get.

You should be more concerned with your video card and RAM.

If you're planning on using this comp as your main computer as well, you could just go all out.

If you are not really into playing and changing your system around, your best bet is to by a dell. Everybody who is into computers would say build you own for desk and name brand for lap, but really, dell supplies support and repairs that could be very helpful to you down the road.

My opinions are as follows:

1. Stay away from media center, it will severely limit your ability to use your computer in a work enviroment, (no networking) and no matter what you do, which OS you decide to upgrade to later you cannot ever remove media center.
2. Unless you have a desktop, stay away from Vista as it is very VERY resource heavy and even when tuned down negates much of your hardware speed.
3. get the computer with the most possible RAM capacity as this is really more important than processor speed.
4. DVD-RW is a must, (so you can burn that HDTV programming and get it off your hard drive)

5)SATA is easier to work with down the road

6. try to get a dual core, but for what you want/need you don't need cutting edge tech, (ie, if you can get a 2.8 processor for $200 less than a 3.5, go cheaper as you will not be able to tell the difference.
7. as many high speed USB 2.0 ports that you can (for adding fun stuff, printers and external memory)
8. integrated wireless
9. at least one expansion slot
10. NIC
11. monitor out

Good Luck

Apple's Mac Book Pro is an excellent laptop that lets you run every app on the planet.  It has so many cool features like a built in camera and microphone.  The only caveat about getting the larger HD is that you will have reduced throughput speed.  This is the number one bottleneck in todays architecture.