How to deal with large object?

Is there a how-to or a FAQ or deal with large objects?

I am using PostgreSQL 8.0.3 (on mingw32)  and  PSQLODBC.DLL  3.0

I have tried to use BYTEA but the driver gives me back :
type "lo" does not exist
wether I declare bytea as lo or not (in the ODBC driver)

I have tried too to declare :
create type lo (internallength=4, externallength=10, input=int4in, 
output=int4out,  default='', passedbyvalue);
but the ODBC driver answers (in log)
ERROR from backend during send_query: 'ERROR:  function int4out(lo) does 
not exist'
then crashes my program

I am a bit lost in docs...
Thank you in advance
Pierre Couderc