I do something similar from one of my applications.
I create a text file for the day if one doesn't exist. I use the date in the text file name, and then check for the file using a known name for the day, and if it doesn't exist, I create it.
Then I open it and write one line to it using VBScript from Access. The psuedo code is like:
Create scripting file system object
Check if today's file exists
If no, create today's file
Write one line
write one line
This doesn't include whatever you are doing to generate your one line.
I did another similar post on writing to a text file earlier this week. Find that to get started, or post back. I may not be able to get back till Monday.
Look up Scripting.FileSystemObject at MSDN as well.
Look it up at: http://wrox.books24x7.com