Running Total

Ahhhh this is doing my nugget in!!! I have a simple table with 4 fields
ID (unique number)
DATE (date)
CAPACITY (number of SKU we can hold)
ORDERS (number of SKU on order)
the data looks like this

ID DATE CAPACITY ORDERS
1 01/01/2007 250000 250000
2 02/01/2007 250000 300000
3 03/01/2007 250000 300000
4 04/01/2007 250000 300000

So looking at the above table we can see that we have more orders than capacity in our factory, however they require to see this in graph form, so what I need is for each ID a running total of the CAPACITY and ORDERS so over a given date range i would produce a graph to find the "pinch points" where we could see if the capacity is less than the orders we have over time.

so my new table would be:


ID DATE CAPACITY ORDERS CAPRUN ORDRUN
1 01/01/2007 250000 250000 250000 250000
2 02/01/2007 250000 300000 500000 550000
3 03/01/2007 250000 300000 750000 850000
4 04/01/2007 250000 300000 1000000 1150000

etc. which i would create my graph from. Ive looked at Dsum and some other methods but cant get my head around it so any help will be much appreciated.
Thanks Steve.