update stock levels on insert

hi all,

i have an insert record using dreamweaver which inserts parts used into a table in the database.

at the same time of the insert i would like to trigger an update record in the stock table which will automatically reduce the quantity of that stock level by the quantity entered in the insert record form.  could you help.

the other part of this is that the stock level has 2 elements to it which is unit stock and van stock so it would need to update based on the insert record form drop down box which will be "Unit" or "Van" options then deduct from there?

appreciate any help.

cheers