poor performance in migrated database

I have migrated a database from MS SQL to a
postgresSQL database, but when running it, the results
are very slow (and unusable) which is the only reason
we don't entirely move to postgresSQL.
The problem is that there are many nested views which
normally join tables by using two fields, one
character and other integer.
The biggest table has about 300k records (isn't it too
little for having performance problems?)
What could be the poor performance reason? the server
is a dual itanium (intel 64bits) processor with 6Gb of
RAM and a 36Gb Raid 5 scsi hdds of 15k rpm.
If someone has the time and wants to check the
structure, I have a copy of everything at
http://www.micredito.com.sv/.carlos/materiales.sql.bz2
it is a pgsqldump made with postgres 7.4
Thanks in advance for your help.

Carlos Lopez Linares.

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Ing. Carlos Lpez Linares
IT Consultant
Quieres aprender linux?
visita http://www.aprende-linux.com.sv

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