Hi,
sorry it's been awhile since I last installed XP so I obviously didn't get the 'timing' right 😉
XP needs to be at least at SP2 level in order to work with BootCamp and can be installed on a Mac.
XP SP1 discs show a far odder behaviour then your problem.
If you have access to a Windows PC you can make yourself a SP2 or SP3 install disc from your SP1 disc by following these instructions
http://www.winsupersite.com/xp/sp3_slipstream.asp
And no there is no way to swap discs halfway through the installation.
Or try making a full-disc copy of the XP SP2 discs you have (using CD-RWs so to not waste money) and use the copy for installation.
I use SimplyBurns in OSX for such copying.
Regards
Stefan