I'm not Cathe but I thought I'd chime in:
First of all, congrats on your decision to get in shape with Cathe! A few suggestions:
Start with her Basic Step and Body Fusion DVDs produced in 2004. Consider also getting Low Max from her new Hard Core production just released. Consider also getting at least one of her total-body strength training workous such as Muscle Max from the Hard Core series, or Maximum Intensity Strength (which is combined with Power Hour and Body Max on one DVD) or her Muscle Endurance workout (which is combined with Boot Camp on one DVD). Be very judicious with the total-body strength routines, beginning with very light weights and work your way up; maybe just do the reps without weights to get the feel for them.
When you are comfortable with Basic Step, Body Fusion and/or Low Max, consider bringing in kickboxing. Cathe has produced many good kickbox routines that are fairly medium in impact, such as the Cross-Train Express (CTX) Kickbox workout, the Cardio Kicks workout, Kick Punch and Crunch from the Body Blast series, and Kick Max from the Hard Core series. There are high-intensity blasts on each of these routines; you're encouraged to make impact and intensity modifications on these while you work your way into them. Beyond that, the sky's the limit!
A-Jock