I updated my gf's system from a socket A mainboard to a socket 754 board without reinstalling Windows. The way I did it was before making the switch I went the Start -> Settings -> Control Panel -> System -> Hardware -> Device Manager. I then uninstalled every peice of hardware related to the mainboard and chipset (I also nixed the graphics driver as well, just to be thorough). Note that "every peice of hardware related to the mainboard and chipset" includes things like integrated sound and ethernet devices, memory controllers (if your board predates AMD's integrated memory controller), SATA/RAID controllers, etc., and possibly also the CPU if you are swapping that out. I then swapped in the new board, making sure to hook everything up the exact same way as it was on the old board (when applicable)...for example, if a drive was connected to the promary IDE channel on the old board, it went on the primary channel on the new board as well. I then powered on, configured the new board's BIOS, set the correct boot device, and everything magically worked, all I had to do was install all the drivers and it was good to go, no reinstall of Win XP or other programs necessary.
That said, I'm not sure how HP's Win XP distribution will behave. If it is Win XP Home (instead of Pro), then there's already virtually no hope, as I believe that Home monitors for hardware changes and will disable itself if it finds that too many things have changed. If, instead, you have XP Pro then it's possible it will work.