This means that you either have a typo when inputting your product key or you installed Windows XP Home with a key from another version of XP Home. There are OEM releases of XP, Retail versions, and Volume Licensing versions. In other words, your key is mismatched with the CD use are using to install.
The other possibility is that you misread one or more of the characters in the Product key. 8's can look like B's, 0's are always zero, not the letter O, and G's are sometimes misread as 6's.
Especially check the 8's and B's.
Otherwise you need to find a matching install disc for your key.