A.
If you have personal or "sesitive" information or files that you wish
to be completely erased then I would look for a freeware or shareware
utility that will overwrite the hard drive with alternating patters of
1s' and  0's then 1's then 0's (several repetitions).

Even then, there are forensic utilities that might recover data from
the disk.

Donate the computer along with the Windows CD, floppy boot disc, and
any printer driver floppies, video card drivers, etc that came with
the machine..  Let the new owner install Windows.

B.
On the otherhand, if you are not so concerned, and the system is
functioning without error, I would not bother to reinstall.  Donate
"as is"

C.
If you wish to reinstall, make sure that you have a floppy boot disk
and a Windows install CD and any printer driver install floppies, etc
before you begin.

If the drive was wiped, boot to dos with boot floppy - insert Disk 1
of floppy set and type "  a:\setup   "
or insert Window 95 CD and type "  C:\win95\setup  ".

If the drive was not wiped I would at least reformat the hard drive
before install.

Hope this helps a bit.

Lee