Hi, Welocome to the forum. You ask some good questions, so to help others I will try to answer them all in one go...
1. Will any hdd work? can someone tell me specifically what type of hdd i need to get (rpm, size?)?
Most 2.5 inch laptop drives will work - must be parallel ATA interface. Speed is not an issue. Very fast drives (7200 rpm) are best avoided due to heat. 5400RPM and below generally OK. Bigger cache memory is better (8MB is good) but many here including me have drives with small 2MB cache and they are OK. Makes in common use include Seagate, Toshiba, Hitachi, Western Digital.
2. what is this talk that phatbox is dead? awhile back i saw them sold on online stores, now i only see them on ebay.
The Phatbox is not that widely promoted now. Phatnoise had in the past done deals with big car makers, and most of the cheap boxes came on the market when VW/Audi decided to drop this as a promoted item. The dealers then let their stocks go at bargain basement prices. There is very little news coming out from Phatnoise. The trends among the OEM suppliers to the car makers are to start to include some of the features in the box into new head unit designs (and many folks want to plug in their iPod for example rather than to have a specialist box just for the car).
3. i have located the 13pin cord in my trunk... is this the only requirement for installation? is audio passed through this cord as well?
I am not an Audi owner. However, if this is the CD changer cable then the answer is yes.
4. i have located a phatbox here on ebay: link
will the hdd mod work on this model? What am i looking for exactly when talking about hdd mod compatibility?
The hack process for VW and Audi boxes is normally OK. A few people have had issues, but there are known work-arounds to get the hack to complete. If you stick to a box intended for VW or Audi then you should be OK from the hacking point of view. If you get an Audi box you are most likely to end up with the right cables - otherwise you will have to get these separately. Another important thing to look for is that the box is sold with a DMS cartridge (most are sold with 20GB as standard), a docking cradle (if you buy one separately the USB2 version is recommended over USB1), and you should also be sure to get the software CD.
5. what is a good price for the 20gb model posted? i remember back seeing them for $150. any site to buy them cheap at?
Prices are a bit higher than they were a year ago. $150 - $200 for a complete outfit like this seems pretty good value to me.
6. is there anything i should know in addition to what is mentioned in the tutorial?
Probably - but best to take the plunge and get the thing installed. The only common problem is that when you come to do the hack, you may need to corrupt a file called ramdisk.sig if the hack does not complete automatically. Use the search tool on the forums. There is lots of help on this specific issue.
sorry for all the newbie questions...
We were all newbies once...!
I have had my Phatbox installed for a year now - very largely thanks to this forum - and it is the best thing that I could have added to my car. I wish you every success.