Request for thoughts...

I'm thinking of starting a little project of mine, that would have, as
core functionality, the capability of doing general substring search
(thru regexp) on a large number of records (say hundreds of
thousands), using a free-text field as key.
I know that this is not exactly what SQL DB are built for. However, I
would like to use PG as the "container" of this data, possibly
coupling it with a web interface (PHP).
There's anybody that would like to share some thought/discussion
about what tecniques could be used to realize this in the most
efficient way?
Some other specification:
*Researches should be made on 1 or 2 fields, containing generic
text
*The clause of the search should be a generic regexp (I'm not
talking of a free text search)

Thank you in advance for any hint, and my best regards to all...

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Fabrizio Ermini Alternate E-mail:
C.so Umberto, 7 faermini(at)tin(dot)it
loc. Meleto Valdarno Mail on GSM: (keep it short!)
52020 Cavriglia (AR) faermini(at)sms(dot)tin(dot)it