lock problem when dont commit

Hello

I use postgresql 8.0.1 under windows and jdbc3 with new java tiger...

i work on a database with manuel commits and rollback..

my problem is when 2 people work in on the same time on the database:

---table liefAdress-------------

pseudecode

client1:
...
conn.setAutoCommit(false)
insert into liefAdress(adress,postcode)
//id is autoincrement
insert into liefAdress(adress2,postcode2)
....

client2:
insert into liefAdress(adress3,postcode3)

--->here is the problem user1 dont commit his
transactions.. the client software are locked..
you can do nothing in the programm..!!

client1:
conn.commit()
//all the adresses are inserted

client2:
the adress is also inserted and the
java clientsoftware is unlocked...!

my question is why the java programm from client2 is locked???
can I say to the connection "when you must wait for the commit of the
other users
bring me a warning" or why the row from client2 are not inserted???? I
dont lock everything.. must i change the transaction mode?? I use the
default transaction mode..

thank you for your answers!!!

Mican Bican