First ask yourself why you would want to do this at all. Unless you are
connected to a large corporate network, or you are a high end web developer
who needs to test ASP code in a local IIS environment (and if this means
nothing to you, you are not), then there is absolutely no reason to upgrade
at all.
Windows XP Home is the same code, byte for byte, as Windows XP Pro. There
is no qualitative difference or advantage to be gained from this upgrade
unless you absolutely need one of the few features offered in XP Pro. For
the very vast majority of users, leave it as is, and spend the money on an
upgrade to Office 2003 or something like that.
If, however, you *do* need one of these features, then an in-place
upgrade is just fine. After all, you are overwriting Windows XP with itself.