If it's a laptop hard drive adaptor you're talking about, use it to install the laptop's hard drive in another computer (preferrably running Windows 98). It should show up in Explorer, where you can format it with the /s switch--this transfers COMMAND.COM to the newly formatted hard drive, allowing it to be bootable.
Once the drive is formatted, create a directory on it (I like to call it CABS) and copy all the install and CAB files off the Windows 98 CD (x:\win98\*.* I think) to the directory. This will allow you to install Windows off of the hard drive.
Replace the laptop hard drive back into the laptop and boot it. It should go straight to the command prompt where you can type
cd cabs (or whatever you called the directory), and then type
setup /ie. This begins the typical Windows 98 install, and the /ie switch skips the option to create a new Windows bootable floppy during setup (which would be rather challenging considering you don't have a floppy drive).
Provided everything works properly to this point, Windows 98 will install just as if it's being done off a CD, though much faster. When the installation is done, I recommend that you leave the CAB files in the original installation directory; if Windows ever asks for the installation CD, point it to that directory (instead of the non-existent optical drive) and it'll find all the source files it needs.
If you need drivers for the X20, you can download them from
IBM's website.
I hope this explains everything. If the post is a bit too wordy, just let me know and I'll try to clarify things.