Create your own XP SP3 slipstreamed ISO. Detailed step-by-step instructions.

If you already have a Windows XP setup disc, you can convert the disc to an ISO file. Download VirtualBox and then install it like you would any software. It's fine to accept all the default options.

The Windows ISO file is too large – Boot Camp Assistant creates a [X] GB installer partition which will contain the files present on the Windows 10 ISO as well as the Boot Camp Support software.