Adding, Subtracting & Totalling hours

I am having real trouble creating a Excel sheet to record hours total worked/owing. I will be recieving timesheets and taking the total time owed/earnt from each fortnight and adding them into the spreadsheet as below,

Estelle Andrew Patty
Start Total 00:00

Period Beginning

30-Jan-12 +01:00
13-Feb-12 -00:30
27-Feb-12 +02:00
12-Mar-12
25-Mar-12
08-Apr-12
22-Apr-12
Flexi Balance +02:30


I would like to do this for each person as its the simplest, most compact way of summing up everyones Flexitime so that managers can open it up, view total time owed/earnt before authorizing time off. Ive searched the net and understand you need to use a custom sum [h]: mm but every time you put a minus in there it errors.


If this isnt possible, I would like to record the data in the following way,


Estelle Andrew
Period Starting Plus Minus Total Plus Minus Total
11-Jan-12 01:00 00:00 01:00
15-Jan-12 01:00 00:00 02:00


With the second example I wouldnt mind if the grand total was at the bottom or if it added on to the total each week. I hope that makes sense, I have been googling for hours over several days and not found an answer or template for what im looking to do.

Thanks very much for any assistance,

Aron

Apologies for the sloppy examples, I seem to be unable to upload a screenshot from work. I am not the best when it comes to excel, by any means.