Hi
I found this which may help you. Just need to modify it.
Calculating yesterday's date on Win9x (DOS batch).
so this batch will do it:
===== BATCH SCRIPT BEGIN =====
@echo off
for /F "tokens=2,3,4 delims=/- " %%a in ("%DATE%"

do (
set M=%%a
set D=%%b
set Y=%%c
)
:: Set today's date format
set TODAY=%M%%D%%Y%
set /A D=D-1
if not "%D%"=="0" goto dateend
set /A M=M-1
if not "%M%"=="0" goto keepyear
set /A Y=Y-1
set M=12
:keepyear
for %%a in (2 4 6 9 11) do if "%M%"=="%%a" set D=30
if "%D%"=="0" set D=31
:dateend
if "%D:~1,1%"=="" set D=0%D%
if "%M:~1,1%"=="" set M=0%M%
:: Set yesterday's date format
set YESTERDAY=%M%%D%%Y%
for %%? in (M D Y) do set %%?=
echo YESTERDAT=%YESTERDAY%
echo TODAY=%TODAY%
===== BATCH SCRIPT END =====
Watch out for line wrapping!
That script will get today's and yesterday's date into the variables %TODAY% and %YESTERDAY%. The format is MM/DD/YYYY, but that can be changed (read commented lines).
That script is only for NT systems. In order to do such a thing in Win9x, I would store today's date to be used tomorrow, instead of calculating yesterday's date.