Show Results After Date/Time

Hey,
I've got to make a query that displays all records whose Date/Time field appear after another tables Date/Time field.
I suppose I could say this is for use in an "Item scanned into inventory, Item Scanned out of Inventory" fashion.

To purpose is to use the total items returned after the date/time to be subtracted from the total of items that were scanned in at an earlier date.

I always tend to get redundant because I'm never sure how well I explain something, it would work something like such:

Table 1(Items Out):
ItemID | DateTime | Quantity
1 1/1/08 1:00 1
1 1/1/08 3:00 1

Table 2(Items In):
ItemID | DateTime | Quantity
1 1/1/03 2:00 1


So effectively the query would run, with the date/time criteria being ItemID 1's Date/Time. It would ignore the 1:00 entry as it occured before the first Item that was scanned in, and return that we have 0 ItemID 1s in inventory.

Inventory is just being implemented it was seat of your pants in the past that is why I have this dilemma we dont know how many are in stock until we check it manually but we know how much has left. This is why data before our manual check is not important to our current totals. We could have sent out 5 ItemID 1s but only have 1 in stock now, and if we use that data we would have -4 in inventory. I'm attempting to use the oldest date/time of the manual scan (table 2) as a criteria per item scanned against table 1. Hopefully, to return the present total of items on hand.

Edit*
As a note, I understand how to use >=#1/1/08 1:00:00# as a criteria but for some reason I cannot swing using a field in a table as criteria. That's pretty much what I can't find on the board or in my books.