I am running TC & TRS2006 ... and due to the receint 04/06 unsupport, I will not be able to upload my routes to the DLS.
However I can download every asset from the DLS, except for 09/10 stuff.
I suppose that 09/10 would take a more superior system than that of my Desktop PC, and that is why I am presently using TRS2006.
Are you planning on building and releasing routes using: trainz railroad simulator 2004 ? For what reason are you choosing the 04 version, might I ask ?
I must add, that Third Party sites will still be able to host your 04/06 created routes, Paintshed, and asset creations.