Suddenly I get another idea about you XP installation disk.
Maybe your XP is duplicated from an original one. If so, you must do that by just Drag and Copy by Nero or some other burning softwares else.
You can not copy an Operation system disk like that. You should use CD/DVD-COPY function, otherwise the operation disk will not autostart anymore. It just likes that you underwent.
Method 1:
1.make a bootable disk (floppy or CD) with the CD-ROM mounted function
2.boot from the bootable disk
then you can setup WINXP from the WINXP install CD whenever you want
Method 2:
1.make a bootable disk without CD-ROM mounted function
2.copy the WINXP install CD to a folder in your HardDisk (under the WINXP running now, "select all"->"copy"->"paste")
then you can setup WINXP from your HardDisk anytime