VBA code for pulling a sequential number from a text file dependent on a form entry.

untested but maybe:

Sub Macro_1
dim fs, fil, num
set fs = createobject("Scripting.filesystemobject")
set fil = fs.opentextfile("J:\stuff\stuff\stuff\POnumber.txt",2)
num = fil.readline
fil.writeline num+1
Range("E8") = num
end sub