Is it at all possible to create a text file, so that when any user opens a particular spreadsheet, their username and current system date is appended to the text file?

I'm inerested in creating an access log for one of our spreadsheets.
I'm no VBA expert, but i'm assuming this might quite straight forward.
Havent got a clue how to get the user's login ID, or Excel User name, so any help will be appreciated.

thanks in advance,
Matt