LOL- I just fixed my cat tree from Fosters and Smith this morning!!
I've had my huge, expensive cat tree for almost 6 years now, and the posts looked horrific. So this is what I did:
Purchased scrap carpet from Home Depot (it would be cheaper at a carpet warehouse, but not by too much). I told the salesperson what I was buying the carpet for and she had cats, so she directed me to a cheap, mid-pile carpet that would be easy to affix to the posts.
I also purchased this staple gun and staple assortment from Amazon:
http://www.amazon.com/Stanley-TR250-SharpShooter-Heavy-Duty-Staple/dp/B000BR2ERO/ref=sr_1_3?s=power-hand-tools&ie=UTF8&qid=1412551724&sr=1-3&keywords=staple+gunIdeally, you could borrow this from someone, but I asked around and no one had one. But it's not expensive and I can use it for a lot of projects.
Then, the actual process:
I ripped off the old carpet from the posts with pliers (the carpet on my Dr. F&S cat tree was just stapled on). I didn't bother disassembling the cat tree.
Take the scrap carpet and flip it upside down, and measure out the rectangles of carpet that you need. You can use the old carpet that you ripped off as a guide, as well. I measured the posted and the length was accurate when I cut, but I added 2 inches for the width. Cut the carpet with a box cutter.
Wrap the carpet around the posts and staple one end from top to bottom, then wrap around the remainder and staple in the overlap. If you want, you can also glue it on, but I think the staples were more secure.
That's it! It took about an hour for the whole thing. Here's an "after" picture of the cat tree: