Are you trying to do a re-install from within Windows, or a fresh install on a formatted hard drive?
This is from setup.txt on the Win98 CD:
"SU99xxxx Messages
SU99 is a prefix that is added to all errors that Setup
does not have a specific error message for. These errors
are often caused by low conventional memory. If you have
already created a Startup Disk, quit Setup, shut down your
computer, insert the Startup Disk, and restart the computer.
Then, run Setup from the MS-DOS command prompt."
If you are trying to re-install from within an existing copy of Windows, you'll either need to shut everything down to free up the necessary memory (may or may not work), or boot from the 98SE CD or from a floppy and do a new install of Windows on the drive (you MIGHT be able to get away with installing over the top of your existing copy, but there's no guarantee it would work, and your third-party programs would definitely have to be re-installed).