Dates in MS Excel

=IF(b1="","",TODAY())

This will return todays date in the selected cell if a value is put into B1. If no value is put into B1, the cell remains blank. Anything you put between the second set of quotes will be returned if B1 is blank. Remember to format the cells to the date output you require.
For example, if you select A1, format the date output you require, then type in the formula, or enter it through the 'if' function found in INSERT, FUNCTION, A1 will remain blank until you enter a value into B1. (Text or numerical). If you do it through functions, you can specify other criteria. eg. if B1<10. Hope this is clear!! I learnt to do it by playing with functions. I am sure if you enter the formula and play around with it, you will see how it works. If you are struggling, send a pm and i will try to help.

Profhig - will the date be static that way, or will it keep updating itself every time the sheet is recalculated?

What this will do is enter or change the date to the date on which the information is entered or modified. Every time the data is updated, the date will update with it. Is this what you wanted? You can, of course enter a range of cells to refer to one cell in which the date will update whenever any of the information is added to.
You can do this with the time, as well, by entering 'now' instead of today and formatting the cells to the output required. This way, if you include seconds in the output, the time will change and you can see instantly what effect the formula is having, and modify it accordingly. Then, when you have what you want, you merely change 'now' back to 'today', and reformat for the date output.
I hope this is clear. I am not very good at explaining it. Don't hesitate to ask again if I've confused the issue!!! (I could always email you an example, if you want.)

I was just a bit confused. I've used TODAY() for date stamps before, but then had to copy & Paste Special > Values so that when I open the sheet up at a later date, the dates are fixed at the time when I made the entry, and not the date I openend the spreadsheet. Otherwise, if I make an entry, say, today, if I open the sheet at Christmas, will it say 12/10/04 or 25/12/04?

I see what you mean. I will try to find an adequate formula, but for this I think you will need to run a macro. I suggest you look HERE
An alternative to typing the date or using a macro is to use ALT + ;. This will return the date in the format you specify through the format menu. I hope I have been of some assistance. Sorry I can't help you with macros. I am not too clever with them, and can't seem to find the time to investigate the subject. Good luck!

Thank for your help, Prof. If I have any luck I'll come back as well.