I would do a 5 minute warm up regardless.. hit the weights and then if you really want do your cardio. Just remember.. If you work out for 1.5 hours or so.. then do cardio for 30 minutes, you are going to be running the risk of lbm loss.. And if you are one of those protein/mrp shake during the workout types of people, you are going to be lowering your GH levels.
Depending on how often each week you like to do cardio, i would switch back and forth between cardio and lifting days. Thats just me. If you run 5 days each week it would be hard to alternate.