Your code "for /f "tokens=* delims=" %%x in (a.txt) do echo %%x" will work on most Windows Operating Systems unless you have modified commands.
So you could instead "cd" into the directory to read from before executing the "for /f" command to follow out the string. For instance if the file "a.txt" is located at C:\documents and settings\%USERNAME%\desktop\a.txt then you'd use the following.
cd "C:\documents and settings\%USERNAME%\desktop"
for /f "tokens=* delims=" %%x in (a.txt) do echo %%x
echo.
echo.
echo.
pause >nul
exit
But since this doesn't work on your computer for x reason there is an easier and more efficient way of doing this. Using the "type" command.
@echo off
color a
cls
cd "C:\documents and settings\%USERNAME%\desktop"
type a.txt
echo.
echo.
pause >nul
exit
Or if you'd like them to select the file from which to write in the batch you could do the following.
@echo off
:A
color a
cls
echo Choose the file that you want to read.
echo.
echo.
tree
echo.
echo.
echo.
set file=
set /p file=File:
cls
echo Reading from %file%
echo.
type %file%
echo.
echo.
echo.
set re=
set /p re=Y/N?:
if %re%==Y goto :A
if %re%==y goto :A
exit