Forms and Table update

[SQUILIKI]

I have tow tables:
Orders and Serialnumbers
The orders tables have the fields: Ordernr,linnr, Partnr, quantity
The serialnumbers table have the fields: serialnr, ordernr, linenr.

the order table contains orders for parts that require serial numbers. At
the timeof order,I know what serial numbers were sent with the order. The
serial numbers reside in the table serialnumbers.

What I would like to do, is open a form with a pull down menu that grabs
and ordernr from the order table and finds the quantity for this record.

Then I want a subform that allows me to go into the serial number table and
identify the serial numbers that were used for this sale and write the
ordenr and linenr in the serialnumbver table.

I can do the pull down combo box fine in the mainform. What I do not know
hw to do easily is develop an acess to the serialnumber table which allows
the user to pick and choose the used serial numbers ( pull down menu, data
view??) but it should only allow the same number of serialnumbers to be used
as the quantity in the orders record.

Any suggestions?
Thanks,
Steve