As a Cathe "newbie" myself, I've found that Step Blast and Rhythmic Step without the step have been great cardio workouts to start with. Body Fusion has also been good to start with...not too simple, not too hard. Do with a step or without.
I actually like the Pyramids for beginning weight work...but I use dumbbells instead of a barbell, and have started out keeping the weight light. I also do the modified lower body work instead of using the stability ball. I still get a killer workout. I also REALLY like Lower Body Sculpt off the Body Fusion DVD.
I'm getting ready to start the Slow and Heavy upper body series, and will be using light weights to start out. I also just started doing Power Hour abs. That's great, although I don't do the planks.
I think that these are great routines to give a beginner a well-rounded workout rotation as long as you don't use heavy weights or a high step.
Good luck!