There is no difference between Premium and Pro, only today have I heard people say there is a Pro 360 pack and if you google "premium pro 360" you get a load of links advertising the one 360 as Premium slash Pro.
If you do invest in one, as I've said before in the thread ( but I'll say it again for you, seeing as you're interested in playing FIFA online with us

), you're best to buy one from a local store so that if anything goes wrong you can get a replacement on the day. Plus you might get yourself a few quid off if you buy one with a game or two (I'd recommend FIFA 08 obviously, Gears Of War is a brilliant game, Mass Effect is a huge, huge single-player game that I love, Bioshock is a great single-player game that can be quite eerie and funny at the same time [great combination], CoD4 is great online, and if you can wait until next Friday Rainbow Six Vegas 2 is going to be a massive online game - sports-wise Virtua Tennis 3 is good, if not devilishly hard, and Table Tennis is genuinely a great little game if you can pick it up for £10 or less, but don't be tempted by Tiger Woods 08 unless you're happy hitting 400yd shots after you finish the challenges).
All the models you pick up from a reputable shop now will have HDMI ports in them, they added that in the early part of last year. You can always ask the guy behind the counter if their 360s have HDMI ports, but I would doubt very much that any reputable retailer would have year-old stock.
To play online, you need to buy an Xbox Live Gold subscription - you can get 3-month, 6-month and 12-month. It's a card with a panel on the back that you scratch off to reveal a code. You click "join Xbox Live" on the 360, you pump in the number, put your address, pick a gamertag, pick a purdy picture and that's it.
As has been said already by Plan M, buy the subscription off eBay, and you can save yourself a packet. In the shops a 12-month subscription can cost you £40, from the likes of
Gameplay.co.uk you can get that down to £30, but you can get one from a reputable seller on eBay for even less than that. You can even have the code emailed to you on the same day from some sellers, which is nice.