Upgrade Presario SR1799AN to Windows XP Pro

Hi
I recently bought a Compaq SR1799AN desktop computer which has an AMD Athlon
64 X2 Dual Core Processor and 2GB RAM. It comes with Windows XP Home
pre-installed.

I tried to upgrade to Windows XP Pro with an upgrade package I bought from a
computer store and the installation seemed to be going
smoothly until the system tried to re-boot. As soon as the computer began
restarting a blue screen would appear only for an instant (so I couldn't
read what it said) and then the computer would try to restart again. This
process would just repeat in what appeared to be an endless cycle. I
recovered the system back to the factory XP Home installation with the
recovery disks I had made.

When I contacted Compaq Telephone Support they told me that their OEM
version of Windows XP Home cannot be upgraded to Windows XP Pro and blamed
Microsoft for this. I can't believe that Microsoft would close the door on
so many potential sales of upgrades to people who buy brands like Compaq, HP
and all the other major companies who bundle OEM versions of Windows with
their computers.

Could somebody please advise if what the Compaq people told me is correct or
are there in fact other issues with upgrading Windows on this particular
machine.
e.g. When installing I chose the "Upgrade" option - should I have chosen
"New Installation"?
Thank you for your help.