Dual Boot

It might be possible but it is not recommended. XP has a file called boot.ini that is configured upon install if you have other OS's. The microsoft recommendation of dual boot scenerios is oldest first, newest last. ie. 9X then 2000 the xp.

Sorry for the bad news...

SLM

You should be able to achieve this by using a utility such as Partition Magic. You'll need to hide the XP partition and mark the ME partition as active. Install ME and then bootmagic (from the PM disk). Once you've set up bootmagic you should be presented with a boot menu at startup. A word of warning though, be careful when doing this and I would recommend creating a backup image and practicing on a non critical system.

Get yourself a copy of System Commander7 it will let you install any OS regardless of already installed OS's especially XP.

It does both multi booting & handles all your partitioning needs, here's a brief description.

System Commander 7 has been updated to include ActiveFS? technology. This allows it to be installed to any Windows or DOS file system, including FAT/FAT32 and NTFS. System Commander 7 is the only OS Manager that can natively install directly into NTFS from Windows NT/2000 and XP. It also sports a polished new graphic boot time interface that is "skinnable" via custom skins available from VCOM's website. System Commander 7 was specifically designed to work with Windows XP, and it includes a complete version of VCOM's award winning Partition Commander 6.0. Partition Commander 6.0, the most powerful partitioning tool available, is completely integrated into System Commander 7 and can be activated from the included self-booting floppy and CD.