In a normal (windows only} installation, windows will be installed in a
primary partition, and the partition must be flagged active (bootable)
If the computer was set up as dual boot, it is possible that the windows
partition was not flagged as active, since LILO doesn't depend on
the active flag to find the OS, but can boot which ever partition you
select at boot time.

If you can boot to a DOS prompt and run FDISK, you can check if the
windows partition is active, and if not, make it active. You should
be able to do this from a win 98 boot floppy. I don't know if the
windows install CD will do it without insisting on doing a reinstall.

If you have the latest Norton Utilities, you can boot from the NU CD
and probably do manual editing of the master boot record (if you
knew what to look for)