You dont need a hardware decoder...My celeron 400 and windvd200 play DVDs with 0 problems. If you want to save power you dont want to put in more cards.
Video...TNT2 w/tv out are cheap and great. Several companies make em...I have a Nvidia w\Creative drivers. Hop on Ubid.com and pricewatch, you can probably get one cheaper there than in a store. And if dont mind buying form Joe Schmo, try ebay.
TV\Radio...search the forum...I think there is a topic now about them. They are getting cheaper and cheaper...
ALIO...Alot of those ALL in One cards dont perform all that great. Make sure you find someone who has it before you buy it.