Stagestep makes a 4 x 6 ft piece of aerobic flooring that sells for about $120 I think. It is a thick piece of vinyl-like stuff, about 1/2 inch thick or so, and can be rolled up. It claims to be resilient and absorptive for high impact activities, but I would caution you guys working out on carpet that if there is concrete under the carpet, there is going to be a lot of impact transmitted to your knees. I exercised on my carpetted basement for five years and it really killed my knees. Anyway, these pieces will slide over carpet - I bought the rubber mats that go under carpet over carpet and it held them fairly well, although they still slid somewhat.
I purchased the foam blocks and a piece of Quietstep from Stagestep, and my husband and I constructed our own little aerobic floor 8 x 8, and it makes all the difference in the world for my knees. We have laid it right over the carpet and can take it apart should we ever move - they also sell this semipermanent tape. I am back stepping with Cathe - last year at this time I had to bow out of the Cathe trip because my knees were so bad. I think the link to Stagestep is
www.stagestep.com - it is also somewhere on this website. This option cost probably around $300 all total, but for me, very worth it.
Cheers!
Colia