If it is not RAID, I tell you to connect it to another computer as secondary
disk, but with RAID it is not as easy as with single disk.... If you have
such possibility, connect it to NT 4 systems only! W2K and WXP systems can
make irreversible changes to your NTFS partition structures making them
unaccessible for NT setup repair procedure and, in case of lack of
servicepack level, also for installed OS itself (you need at least SP4 for
NTFS partitions affected by W2K and at least SP6 for partitions touched by
WXP).

It may be possible to connect another disk to your system, make it primary
and install emergency OS instance to it, but in such case not all files in
temporary instance could be used to replace corrupted files of original one.

Installing of secondary OS instance is standard procedure, recommended by
MS. You need only 150MB of free space to install minimal NT4 OS instance
(standalone server or even workstation is enough, no network needed except
if you want to use any network based drives or backup devices), but better
if it is 300MB as you probably need also to apply servicepack to this
instance to get right version of files you need for replacing. It is,
however, possible to extract right version of files from installation or
servicepack media, but you need to know exactly which one (and it is not
always easy in case of hal, because hal.dll is renamed copy of driver file
specific to your system and its current settings). Secondary OS instance is
consuming only space, it does not affect runtime of original OS instance or
its appplications. Also this secondary OS can be easily wiped out after
repair, if you really need to get this space back. But IMHO it is really
better to keep it installed as it really speeds up troubleshooting and can
short server off-time by hours.

As it is NT4, you can install another OS instance also to the same partition
as original system but to another folder (ie. not to default WINNT). For NT4
systems it is safe to have more OS instances on the same partition, even
this is not recommended because all such instances are sharing common
folders under Program Files tree. So you need to use prefferably the same
version of OS (or as close as possible) and you should to install the same
version of MSIE, apply the same level of servicepack and also all hotfixes
and security packages to all of them.

Note: If your server is multiCPU or if it is new hardware with
hyperthreading, check your BIOS settings carefully as it is possible your OS
is now detecting different  number of CPUs then your current hal driver is
written for.

If your C: partition is FAT16, you can start from MS-DOS system floppy and
replace files by its command line. If it is NTFS, there is available NTFSDOS
driver tool on net, able to allow you to do the same thing.