There is a few ways you can fix this problem.

Windows 98 startup disk will not allow access to an NTFS-paritioned hard drive. Therefore, you will not be successful with this.

The EASIEST way would be to do a install of Windows 2000. It will search your drives for previous version of Windows and offer to repair or do a fresh install. I would repair. This will allow you to keep your files and programs. You need to change your bios settings to search for your floppy, then CDROM, then go to your primary hard drive. Once this is set (usually, this is the default BIOS setting), you can restart your computer with the install CD in your CDROM. Let the setup run its course and follow my previous instructions.

If you are completely desparate and want to do something tricky, here you go (this will require you to boot with the install CDROM and choose the recovery console):

At command prompt, type:

DIR \HIMEM.SYS /S

exactly as shown here.
Hopefully, it will show you where HIMEM.SYS resides.
Example
C:\DOS\HIMEM.SYS
C:\WINNT\HIMEM.SYS

Type exact that line into C:\CONFIG.SYS, replacing older versions of
it:
DEVICE=C:\WINNT\HIMEM.SYS

Save C:\CONFIG.SYS and reboot (important!).
If Windows still fails to load complaining about a missing HIMEM.SYS,
try the DOS version. Replace the line

DEVICE=C:\WINNT\HIMEM.SYS

with

DEVICE=C:\DOS\HIMEM.SYS

Save C:\CONFIG.SYS and reboot.

If it still fails, you'll have to get HIMEM.SYS from either your
Windows or your DOS installation diskettes. You can also copy it from
the C:\WINNT dirctory of some other machine.

In that case, rename the HIMEM.SYS file from the C:\WINNT directory
to something else, e.g. HIMEM.OLD and then copy your new HIMEM.SYS to
C:\WINNT .

Make sure you have a line

DEVICE=C:\WINNT\HIMEM.SYS

in your C:\CONFIG.SYS , reboot.