Mysterious locking problem

Hi,

I'm having a misterious locking problem ( caused by a transaction, i think ).
But for my understanding of transactions and lock's, this wasnt supposed
to appen.
I'm using Postgresq 7.1.2 on a Suse 7.x box.

I notice the locking problem when there are two 2 different queries
running, of different connections( initiated by PHP ).
Lets say I have 3 Tables:

- Table A, B, C

The query that is executed by one of the connections is a select on table
B( to get some foreign keys values ) and an insert in table A( just after
the select ).
The other query that the second connection execute is an insert into
table C( to start this insert it does some selects in table B ).
Every connection is executed inside a transaction.

I have tried getting the internal state of each transaction....but i
havent find docs about it( i have seen docs for 7.2.1 - Monitoring ).
Can i inspect the state of a running transaction in 7.1.2?

Does any one have any hint?

Thanks
Miguel Carvalho