Linux and Windows XP on the same PC

I have to get Linux and Windows XP running in the same PC. For a number of reasons that are not relevant here, I have to start from Linux already installed. This must be preserved as is. Please do not suggest to back it up and do an XP, then Linux, installation from scratch. The Linux already installed must be kept as is, period.

With such a constraint, the following questions come to mind:

1) Must XP be in the first parbreastion of the first disk? Must it be in the first disk at all?

2) Must XP take over the whole of the first disk, or can this first disk hold a parbreastion for XP, and one parbreastion, or more, for Linux?

3) Can in general the boot process be controlled by LILO, even if Linux is installed on a disk other than the first one?

4) My understanding is that, when XP is installed, it removes whatever boot loader was in place, installing its own instead (par for the course for MS, for whom the notion of fair play is unfathomable.) If that is true, the preinstalled Linux will become inaccessible. Would it be possible to boot off a Linux kernel in a floppy or a CD, mount the root parbreastion of the preinstalled Linux, and once it is up and running reinstall LILO, with the appropriate incantations for both Linux and XP?

As you can see, the goal is to try and install XP, side by side a preinstalled Linux, so that then we can boot either XP or Linux, as LILO enables one to do.