I'm going ask a stupid question, I know this is going to be a stupid question, but I don't get it. To do what you say you want, it seems to me you use the following steps:

1) Have a full week (Monday's date) in column A.
2) In column B write a short description of the work done.
3) You're able to write how many hours it took (in column C).
4) On the following row, to populate the next week's date (the following Monday, if that's what you mean), have it automatically calculate the date from the previous row plus 7; that displays the following Monday's date.

For each week you continue adding rows. There you have it: an Excel Work log.

Now, that is so simple that I know it isn't what you meant to ask. But maybe it tells you how to restate the problem...?