First - why are you wanting to upgrade from Windows XP Home Edition to
Windows XP Professional Edition?  (I assume you mean 32bit Professional, not
Professional x64...)

In other words - what is it you are hoping to gain/being told you need?
Encrypting File System capabilities?  Do you need to join a domain?  Do you
need a bit more built-in control over users?  Do you want remote desktop
capabilities?
http://www.microsoft.com/windowsxp/pro/howtobuy/choosing2.mspx

Many who are told they need to utilize Windows XP Professional to do
something - it turns out - would be just fine continuing to use Windows XP
Home edition and perhaps a free application or two to 'make up the
difference' - and in many cases, not just make it up, but exceed the innate
capabilities of Windows XP Professional (or at least they end up using the
same third-party products those who have used Windows XP Professional have
started choosing over the built-in features.)  ;-)

So the above is why I ask why you think you need to have Windows XP
Professional over Windows XP Home edition in the first place...

Beyond that - the transition from Windows XP Home Edition to Windows XP
Professiona Edition is usually one of the smoother 'upgrades'.  It is still
HIGHLY recommednded you perform an additional backup on your system right
before you try - as things can go wrong with ANY major undertaking and not
using the ability a computer gives you of safely storing your data away from
the main system in case of a problem would be unwise.

Simply purchase Windows XP Professional RETAIL and/or UPGRADE version (not
OEM) and put it in your CDROM and choose to upgrade.

Try searching at
http://support.microsoft.com/search/?adv=1
for key words instal upgrade Pro (17 items together)
or something similar.

Unless you wish to join a Domain there is no advantage to installing Pro