Save File as Date

I use the same spreadsheet every day to record where I go, and what time I get there.
I recently discovered "=now()" which inserts the current date and time into a cell. Cool, now when I open my spreadsheet, the date and time is already filled in.
Every day, I still must click, file, save as, and enter a new file name (always today's date) when I'm done for the day. Shouldn't I be able to just close the file, and it saves as the =now() value automatically? I use Office 2007 enterprise. I can maybe explain it better?

How do I automatically save a file with the name of a cell? The cell will have the value of =now(). I do not want to click on file, save as, then change the date everyday (which often I enter an error and can not find a day, or worse, overwrite a day).
So each day, I want to open the same file (ie, DailyTrip.xls) and then have it auto save as =now() value, or somehow the current date. this will not work.... when i review the files for billing, and i open the file with the dated name, will it change to the current value of now? this will not work.... all files would end up with saturday's date for file name when I process billing. any ideas on how to make this work?

That might work... Where can I go to learn what any of that means? I tried pulling out the excel 98 book I have, but I couldn't find anything about inserting/installing/using code. I think the book I have is too basic. I am struggling with the F1 help. Possibly a link to a start?
Thanks