Guess what, you happen to know a Home Theater Product Specialist who works for Best Buy.
The in-store feed is actually just a high definition feed. Anyways, one thing you want to make sure to get is a television with the ATSC tuner. That way you'd actually be able to get yer local HD channels for free using an over the air antenna.
For size recommendation: you want to be 2.5 times the height of the screen away from the television. As far as brands, keep away from the Westinghouse. It's a low end brand. The Sony's are alright, and the Sharps have nice pictures too. The Samsungs are a pretty good buy. And LG is usually well priced and stand out with the nicest quality picture.
Keep in mind, they're all on the same feed, so when comparing one to another, it's a fair comparison. But mess with the settings a bit too.
If you decide to go towards a Plasma (which aren't as scary as people make them out to be), then go with a Pioneer if you can afford it, otherwise the Samsungs and LGs are good again.
The main reason to go with an LCD over a Plasma is because of the afford-ability of 1080p, and anti-glare screens. To be honest, 1080p is useless on anything less than 50", unless you'll double it as a monitor. Most Plasmas keep up better with action (like sports and such). Some LCDs, like the Sharps, are getting faster. If yer lookin' for something that doesn't glare, but want it to keep up with fast pictures, check out the LG plasmas. They have some nice features (such as brighter whites, less glare, better side-angled viewing) that can only be found in the Pioneer (but for almost half the price).
Cnet has some pretty good reviews and information for you. The financing is usually pretty good at Best Buy. If you're looking to get a sound system too, check out the financing on Klipsch systems (that ends the 30th). 36 months no interest.

Klipsch makes some excellent speaker systems too. I prefer them over Bose actually. Of course paired with a nice Yamaha or Harmon Kardon receiver.
If you have any other questions feel free to let me know. I love the Home Theater stuff. Which is why I work in the department. The guys at Best Buy better get you set with what you need too. Haha. Just don't let them be pushy... they're not on commission.
It's a shame I can't be there to take you through the whole journey.
