In order to remotely control your trains, you would need to retrofit the necessary electronic boards in your locomotives, and get the command system to operate them. Unless you are very handy disassembling  your trains and modifying them to accommodate the boards, it is easier to just purchase the newer command equipped locomotives and the http://www.lionel.com/Products/Finder/ProductDetail.cfm?ProductNumber=6-14295&expandBranch=0&Keywords=&CategoryID=115&RailLineID=&CatalogId=command system.
As an alternative to the above system, a newer system called LionChief http://www.lionel.com/Products/Finder/SearchResults.cfm?doAction=Browse&CategoryID=499has been introduced that is a very simple system with just a remote control and no external components. Everything is self contained in the locomotives and remote. This is the future of our trains.

Larry