I am looking to for a standard Userform and accompanying code that will
allow the user to save or load a txt file whose contents reflect data
for a sheet.

The sheet would contain 6 columns of strings.

(in my case, 6 columns of R1C1 strings)

Example txt file

R1C23 , R5C34, R66C2, R2C2, R89C2, R33C34
R1C24 , ...
R5C29 ,...
R4C4 ,...
R39C195 ,...
..
..
..

The VBA code would take each address from the txt file and write it a
column in the sheet for loading, and for saving would take each address
from the columns and write them to the txt file.

I believe I could write all the code and create the Userform (I have
Walkenbach's Power Programming to guide me), but I am sure people have
created something similar before. Anyone have a good place to start (or
some code that does something similar)? It'd be nice to not have to
start from scratch. Also, any pointers on things to watch out for?

I am programming for Windows computers only, so no need to worry about
Mac's different syntex for directories.