I already had XP set up on a Thinkpad T42, and did not want to have to recreate that install from scratch, so I did my homework on installing 98se *after* XP, and was prepared to manually create bootsect.dos, edit boot.ini, and do startup repair to restore the NTLDR after 98se blew it away.

Imagine my surprise and delight to see that after booting to DOS and installing 98se, on reboot I had a boot menu showing XP and 98se, without my having done anything, and booting into XP just worked, without having to run startup repair.

The reason for this miracle, I think, is that I originally installed XP using IBM's factory restore disks. (I prefer this to installing manually - even though the restore disks install a lot of crapware, it is *so* much easier to use them, then uninstall stuff, than to track down all the drivers and install them one by one, not to mention XP from the restore disks comes preactivated, which is a nice bonus now that XP's activation servers have been shut down).

For reasons long forgotten, IBM's restore disks (which are available for many Thinkpad models on Archive.org) create a dual boot setup. Once you create the restore partition and tell it to "restore original factory contents," it creates C: and copies both ME DOS and XP to it. The laptop first reboots into ME DOS, which spends several minutes running loads of batch files (unzipping archives, copying things from C:\IBMWORK to their final destinations), then reboots into XP and starts installing all the drivers and software (and it cycles through several reboots, alternating between DOS and XP, before it finally finishes).

So, when I installed 98SE on that laptop, 98 setup must have seen the multiboot files already existing, and knew how to insert itself into boot.ini and do its install without disrupting the NT boot loader.