Exactly, just pop in the first (install) disc, and boot the system.
hit F1 when the first screen comes up, then choose rescue / repair mode.
Then it will propose several things, one of which is to restore the boot loader. Choose that one, take out the cdrom and reboot (or reboot and take out the cdrom if it won't spit it out).
[edit] darn, this window was left open since before lunch, and already so many chimed in ....

To add something useful: read up a bit on lilo,
man lilo
and you can make your own lilo bootflop -- just change the first line on the /etc/lilo.conf file from /dev/hda (meaning: bootloader into the mbr of the first hd -- and yes, this you can change to /dev/hdb if you are going to take out hda and replace with hdb for instance) to /dev/fd0 and you're set; insert blank floppy and run the command:
lilo
Come to think of it, that is a nice way to create a dualboot system, no mbr bootloader, just the floppy; floppy out of the system, boot to the standard system, floppy in the drive, boot to linux. Hey, that's actually how I do it.

except naturally that I don't dualboot between xp and linux, but between mdk9.1 and 9.2 (well, haven't taken out the floppy in ages)...