AUTO-POPULATE WORKBOOK WHEN OTHER WORKBOOKS ARE CHANGED

I have a situation where 4 people have individual workbooks that they track
their daily work. Each of the 4 workbooks have tabs for each month of the
year, which they then track items such as Date Received, Customer Name,
Account #, Order #, Due Date, Ordered By, etc.

I am trying to find a way to summarize each of their individual workbooks
into a summary workbook which would also contain monthly tabs. For example,
the summary workbook would contain the same 12 monthly tabs that the 4
individual workbooks contain. When agent #1 enters data on their own sheet
on their February tab, the information is automatically populated on the
summary workbook February tab. The same would apply for agent #2, 3, and 4.

I've created other workbooks, such as vacation tracking, where I have a
summary sheet that reflects each months vacation for each employee all on one
sheet, then a separate tab for each employee showing the 2010 calendar year.
As they enter any vacation time on their own calendar it auto-populates on
their row for the same date on the summary sheet. That was a simple formula,
since each person has their own row to populate the date.

What's confusing me is how do I tell Excel to populate the next blank line
on the worksheet with the information from one of the 4 individual sheets,
since each of them would be entering data through out the day each day.

Is this possible, without creating an actual database? Is there some simple
VBA script that could be written?

Help!!!

Thanks.