Coding issues

Question

My database is in MS access 2003. Am working on a windows application. I have 2 forms namely CIR form and purchase order form. Now i have the common field in both of them as CIR no. The whole process is like this that before going for purchasing we create a CIR for any number of say laptops and then as per the requirement we will create the purchase order. Lets say i have created the CIR for 10 laptops and then in the next month i need to purchase 5 laptops then i will use that CIR no in the next form and will create the purchase order for 5 laptops. Now that CIR No say its 01 is created for 10 laptops purchasing but we used it for 5 laptops so that is still available for 5 laptops. Now say in next month we want to purchase 2 laptops then we will use the same CIR no for creating the purchase order for 2 laptops now CIR No. 01 is left with 3 laptops. Now if in the 3rd month we want to purchase 6 laptops then CIR 01 is having only 3 laptops left for purchasing so we will use it for 3 and then again create a new CIR for say 10 laptops and will use that for remaining 3 which are to be purchased. Means it should do the counting process also. 

CIR form has following fields : CIR No, CIR Date, System Type, Quantity.

Purchase order form will have fields : PO No. , CIR No., PO Date, System Type, Vendor Detail.

 Please help with coding also as am new to this coding world.