Neverending query on 6.5.0 over Solaris 2.5.1

Hello:
    Maybe somebody could give some clue about what is happening:

    I have 6.5.0 running over Solaris 2.5.1 SPARC. I have a
database with 5 tables, 3 of them < 100 regs. and 2 ("usuarios" and
"passwd") with >10000. When querying for:

SELECT u.nombre_cuenta, per.nombre, pas.clave_cifrada,
pas.clave_plana, u.estado FROM usuarios u, perfiles per, passwd pas
WHERE (u.perfil=per.id_perfil) and (u.id_usr=pas.id_usr) and
(u.activa) \g

    postmaster starts eating a lot of CPU and it doesn't finish to
process the query in +20 minutes.

    Postmaster shows:
[3]ns2:/>su - pgsql
Sun Microsystems Inc.   SunOS 5.5.1     Generic May 1996
[1]ns2:/usr/local/pgsql>bin/postmaster -i -d 2 -N 8 -B 16 -D
/usr/local/pgsql
/data
FindExec: found "/usr/local/pgsql/bin/postgres" using argv[0]
binding ShmemCreate(key=52e2c1, size=359424)
bin/postmaster: ServerLoop:             handling reading 5
bin/postmaster: ServerLoop:             handling reading 5
bin/postmaster: ServerLoop:             handling writing 5
bin/postmaster child[2934]: starting with
(/usr/local/pgsql/bin/postgres -d2
-B 16 -v131072 -p operaciones )
FindExec: found "/usr/local/pgsql/bin/postgres" using argv[0]
debug info:
        User         = admin
        RemoteHost   = localhost
        RemotePort   = 0
        DatabaseName = operaciones
        Verbose      = 2
        Noversion    = f
        timings      = f
        dates        = Normal
        bufsize      = 16
        sortmem      = 512
        query echo   = f
InitPostgres
StartTransactionCommand
bin/postmaster: BackendStartup: pid 2934 user admin db operaciones
socket 5
query: select version();
ProcessQuery
CommitTransactionCommand
StartTransactionCommand
query: SELECT u.nombre_cuenta, per.nombre, pas.clave_cifrada,
pas.clave_plana, u.estado FROM usuarios u, perfiles per, passwd pas WHERE
(u.perfil=per.id_perfil) and (u.id_usr=pas.id_usr) and (u.activa)
ProcessQuery
bin/postmaster: dumpstatus:
        sock 5
bin/postmaster: dumpstatus:
        sock 5


    Any hints?

    TIA and kind regards.

Fernando P. Schapachnik
Administración de la red
VIA Net Works Argentina SA
Diagonal Roque Sáenz Peña 971, 4º y 5º piso.
1035 - Capital Federal, Argentina.
(54-11) 4323-3333
http://www.via-net-works.net.ar