You are going to need a floppy-drive that is accessible at boot-up, or a CD boot option...(both are set via the bios).
Failing either... then you could use a drive adapter that accomodates a small (2.5 inch?) laptop drive. This is then installed in another PC. There you can remove NT installation (via delpart.exe or '98 Fdisk option), then reconfigure the drive afresh and format it as fat32. To make the drive bootable to a c: prompt, either use the usual " sys c: " - no " " - routine from a '98 bootdisk prompt; or when you format it use the command:
format c: /s
Once it is formatted and bootable to c: , copy over the '98 cab-files etc. from the '98 CD.
Afterwhich restore the drive to the laptop and run set up from the drive direct.
You could also install CDROM drivers too; this would allow you to run setup from a CDROM if attached/installed?
But perhaps the company can/will help you wipe the drive and install '98? Also I'm surprised they didn't clear this drive out fully prior to handing it over... Security???
There should be an option in the initial POST sequence that allows you to press a key (or keys) to gain access to the bios setings. If luck is in your way you should then be able to set a CD boot option? However whilst most '98 CDs are (usually) bootable, they do not have the same Fdisk/format (equivalent) options included unlike W2K/XP/NT CDs. So you would still need to address that issue; and that puts you back to the start of this post - use a drive adapter etc...
Was there ever a floppy for this laptop; if so has the firm got one they can lend/give you? Failing that a search on the www for the correct one may be useful (and of course Toshiba may have one)???