I have a Pentium 100MHz machine with MS-DOS only on it. What are the basic things that should be in my CONFIG.SYS and AUTOEXEC.BAT files? The ones I'm using came from the Win98SE boot disk, and they give me lots of error messages. Thanks.

There are some basic things in every CONFIG.SYS and AUTOEXEC.BAT and also some things that are unique to each installed program. Try to find and copy back the original installed DOS files before you put the Win 98 files on the disk and restore them. You can edit your AUTOEXEC.BAT and remove the @echo off command on the front and it will display each command as it is executed on your monitor. You can see which lines are getting errors and remove or correct them. Here are two typical files to look at.

AUTOEXEC>BAT
@ECHO OFF
PROMPT $p$g
PATH C:\DOS;C:\WINDOWS;C:\TOOLS
set sound= d:\sb
rem set sbmaster=4044-16656
C:\DOS\mode con: rate=30 delay=2
LH /L:0;1,45456 /S c:\dos\smartdrv 1024 256 /x
c:\tools\sa bold yellow on blue
c:\tools\numlkoff
LH /L:1,13984 C:\DOS\SHARE.EXE

CONFIG.SYS
DEVICE=C:\DOS\HIMEM.SYS
DEVICE=C:\DOS\EMM386.EXE NOEMS
BUFFERS=15,0
FILES=20
dos=UMB
LASTDRIVE=E
FCBS=16,8
dos = high
DEVICEHIGH /L:1,12048 =C:\DOS\SETVER.EXE
SHELL=C:\DOS\COMMAND.COM C:\DOS\ /p
DEVICEHIGH /L:1,19168 =C:\DOS\MSCMOUSE.SYS /2 /A9
STACKS=9,256
DEVICEHIGH /L:1,1824 =C:\DOS\TANSI.SYS
rem DEVICE=C:\WINDOWS\IFSHLP.SYS

If you edit the files to remove bad commands do not remove the lines. Instead, type rem on the front of the line and change them to remarks so you can restore them if need be.

First, you don't need those files to boot. Minimum for the files would be:
Config.sys
DEVICE=C:\DOS\HIMEM.SYS (if you run windows or a ramdrive)
DEVICE=OAKCDROM.SYS (or other ROM driver)
Autoexec.bat
Prompt $P$G (makes dos display directories)
PATH=C:;C:\DOS
C:\DOS\MSCDEX
*******************************************
Beyond this you add lines as you need the computer to do something.