The entry for XP is not incorrect. But many of us delete it.
Here's the prior discussion -> http://reviews.cnet.com/5208-6122-0.html?forumID=44&threadID=37590&messageID=440827 specifically item 4...
One support line says this problem occurs when there is an incorrect entry in the registry that is used by the Disk Cleanup utility to locate compressed files. It offered a way to workaround it through the registry. As a newbie, I fear touching it. I am not sure this is even the answer. Is there anyone who is aware of this problem and how to fix it in a "benign" manner?