Need Help With Data Analysis

Folks,
I need help with this task. I have a set of data that needs to be plotted on
timeline chart.
Example:
Unit ProcStart ProcEnd Machine
U1 5/5/03 6:01 5/5/03 6:04 M1
U2 5/5/03 6:03 5/5/03 6:05 M1
U3 5/5/03 6:03 5/5/03 6:04 M2
:
etc. There are about 40K units and 30 serving machines. The data is in
MSAccess / SQLServer. My overall task is to plot concurrent processing at
each machine at each 1-minute interval.
Example for M1:
count
3|
2| * *
1| * * *
|______________________________
6:01 6:02 6:03 6:04 6:05 6:06

My thought is that if I can break down each row of data into smaller
timechunk, then I can do grouping and counts based on the new data -- which
is something like:
Unit ProcTime Machine
U1 6:01 M1
U1 6:02 M1
U1 6:03 M1
U1 6:04 M1
U2 6:03 M1
U2 6:04 M1
U2 6:05 M1
U3 6:03 M2
U3 6:04 M2
Then I was thinking to do query with: Machine, ProcTime, Count(Unit). Then I
can export the data into Excel and plot it.

My questions:
1) How to break the original data into smaller chunk timeframe (i.e. query,
stored procedure, etc.)?
2) Is this a sound approach? Any suggestions for better idea to achieve the
task?

Cheers,
-Jon