A .dat file is just a common file used for storing misc. info. ICQ, mcAffee, and Kazaa use them for instance. 1 program will not open them all, its not like an .mp3 file. The data can be (and probably is) encrypted depending on the program, however it could be normal text. If you were more specific then maybe I could give ya an answer on what program to use. BTW, even when you "open" a program, it still downloads onto your computer its just in a temp dir and gets deleted. If you dont like keeping the stuff you download then just make a temp folder in ur my documents or wherever and save all your files there. Later, just delete the contents of the folder when your done.