Hello BlueKomet, your post started off asking :-
"My question is this,
What is the compatability of engines and such in the Download station? If I buy 2004 will I be able to download lots of engines and rolling stock? Or should I look for a better video card and get 2006?"
My own opinion, would be to have both installed if you can. It depends on money and storage space available on your PC of course, but recent answers have suggested upgrading your video card, to start with, but are you a creator or just a player of this game ?? As a non-creator personally, I cannot give an honest appraisal of how things are different between TRS2004 and 6 from creative knowledge, I will let our well-educated, genius creators on Trainz comment on that point. But yes, if you purchase TRS2004 you can download everything available on the DLS, apart of course from TRS2006 stuff. With TRS2006 and the patch SP1 installed, you can download virtually everything, HOWEVER, a vast majority of the really old assets might have to be repaired first, through CMP, before you can use them on TRS2006, I hope you have a lot of patience, LOL. If you intend to purchase Trainz Classics in the future, having the working; operational knowledge of CMP in TRS2006, would be a distinct advantage, rather than just going straight from using TRS2004, and as far as I am aware, reading certain comments on this forum, that Trainz Classics MAY still carry certain problems associated with TRS2006 when that was first launched, that have not been completely ironed out yet. I personally will wait, until after TC is made public, to analyse any problems, before I make a purchase.
Happy Trainzing anyway.
Cheers. ex-railwayman.