There are kind of two questions here:
1. Downgrade the version of Boot Camp.
2. Downgrade the OS version.
First of all (since you have OS 10.7.5 installed)…you probably have Boot Camp v4.0.
From this link:
http://en.wikipedia.org/wiki/Boot_Camp_(software)
It appears that Boot Camp v3.3 dropped support for Windows XP. So you would have to use a version of Boot Camp older than v3.3 to install XP.
Boot Camp v3.0 shipped with Mac OS version 10.6 (Snow Leopard)…and I'm not totally sure if Boot Camp v3.0 is compatible with Mac OS 10.7 "Lion". Maybe Boot Camp 3.0 must be used with OS 10.6…and Boot Camp 4.0 must be used with OS 10.7.
So then we are left with the option (and if you wanted to)…running OS 10.6 on your MacBook Pro…just to be able to use Boot Camp 3.0 to install XP. Since you have an i7 MacBook Pro (depending on the model you have)…some of the earlier i7 MBP's can run OS 10.6. But later models cannot…so we would need to know your EXACT model i7 MBP.
Of course if you do not want to run OS 10.6 (or cannot because your i7 MBP is too new)…then you have two options:
1. Run Windows 7 on your MBP (instead of XP).
2. Purchase a copy of Parallels or vmWare Fusion…and run XP in "emulation".
Running XP in emulation won't be as fast as using the Boot Camp method…but it will allow you to run XP. And depending on why you need to run XP…running XP in emulation may be plenty fast.
- Nick
p.s. If your head isn't spinning after reading all that…then great!!!
If your head is "spinning"….sorry!