Hey Tishee...
KPC was the very first kickboxing I had ever done... and I fell in love.... I modified all the high impact to low... was very easy to do with this one.... my love affair for KPC is what sent me on my search for more kickboxing... I tried Taebo like I said, and just hated it...
AFter, reading reviews and asking for advice here and other sites.. I tried Powerstrike workouts and they are great. I got the two I have from homeworkout.com. There is a powerstrike.com website, but they send you to the homeworkout.com link for buying the videos. Only the Millineum 3 is on DVD.. the others are VHS. The powerstrike website is interesting though, cause it gives you all the background on the instructors.
I absolutely love Janis as well... the Hardcore Circuit is wonderful... Strike Zone (also VHS only) is great.. I did it for the first time this week. In fact I did my first jump kicks with Strike Zone! Janis breaks down the moves so well, that you build slowly up to the kick and I could do it! I was thrilled.
Both Powerstrike and Janis workouts that I have are much more low impact that Cathe's KPC... (I have Cathe's Cardio Kicks but have not tried it yet!)
I think a beginner, as I am and I am still overweight one at that, would have no problems with any of these. And to answer your question, I try to do kickboxing at least twice a week. I could do it everyday, I love it so much, but I try to keep things varied and I do circuits and heavy weights the other days.
AS to which ones to get... the new Janis with the short 10 minute workouts is more beginner focused... I actually found it a little too easy... The Hardcore Kickbox Circuit is just such fun and and really cued and taught well... you won't go wrong with either of these Janis's.
KPC like I said, is very easy to modify, and is so much fun, and if you get the DVD you also get Legs and Glutes which is a great lower body workout, plus all the premixes on the DVD...
The advice on Powerstrike I got was that M3 was the easiest... I got it first and then M1 but, I think they are about equal in intensity. both about an hour long and will really make you sweat although they are mostly low impact.
So, sorry... I would say get them all!