Hi Davoe - if you are asking me, I have no idea if the parts will fit your 2003 - they will if it has a 545RFE.
The info on what tranny - Glend has a sticker on his which marked it as a 545; I didn't have a sticker on mine, so I got it off the build sheet. You can get a build sheet from your local Jeep dealer or direct from Chrysler (Aus). You have to give them your VIN number, which is on a sticker - mine was on a sticker on the front passenger door!
You may be able to get the sheet over the net - depends, but you still need to put in the VIN.
I got the parts from an independent Jeep dealer over here; they are Mopar parts. You can also get them from Rockauto, and I believe from moparonline (I can't recall the web address). I went for the independent dealer, because although Rockauto's price was very good, once you added in the horrific USPS charges, it actually cost a bit more than from that dealer! On the other hand, a Jeep main dealer (franchised) wanted to charge about £15 more for the bits than the independent guy.
The choker was the cost of the ATF +4. As I said - £68 for 5L is a LOT of dosh - especially when you need 2 cans of the stuff! It is Mopar +4, but on the other hand, I don't have a lot of choice over here. The US lads seem to have a few more options on the ATF front.
By the way, it might also be hlpful to have a look at
http://en.wikibooks.org/wiki/Jeep_Liberty as well, to see if that can give you a steer.
Sorry I can't be more help.