Find one record from table in second table

[dre-logics]

I have Visual Basic 8.0 + MySQL 5.0
I have two tables:

Table1 ( Rental) {Article rents may be on different days}
Articlelnb Artikelrents Daterent
1000 15 1 nov 2009
5000 12 1 nov 2009
3000 10 1 nov 2009
1000 10 2 nov 2009
5000 5 2 nov 2009
3000 20 2 nov 2009

Table1 ( Stock )
Articlenb stock
1000 100
2000 120
3000 100
4000 150
5000 125

First I want search table table stock with article from rental table.
Secound, If article found in rental table a want to reduce stockwith number of Artikelrents from table Rental.

It just so long that we all have had articles in rental table

Thanks in advance
Andre