Trouble with encoding

Hi, I'll be trying to solve this workaround between postgres odbc
8.01.00.03 and VisualFoxPro(VFP) with spanish chars and unicode
encoding.
VFP''ve 2 ways to send info to rdbms: explicit or for reference:
A little example (I think it's easy to understand)
1) conn=SQLCONNECT('odbc_entry','user','pwd')
2) SQLEXECUTE(conn,"INSERT INTO t1 VALUES ('ñ');)")
3) a='ñ'
4) SQLEXECUTE(conn,"INSERT INTO t1 VALUES (?a);)")

1) Stablish connection
2) Works fine (explicit)
3) Var 'a' takes value ´ñ´
4) This doesn't work (for reference)
This issue works with any other rdbms I tryed (M$SQL, MySQL, Sybase),
including postgres odbc 7.03.02.00 on LATIN10 encoding.

Thanks. Alejandro.