Never done it, but you could try using the PX libraries (as far as I know, these cover Paradox versions 4,5,6, and 7, and ship with a brief intro to what is known about the Paradox file format):
http://freshmeat.net/projects/pxlib/...ease_id=144584
A PEAR interface exists, but it requires PHP 5, as a minimum:
http://www.weberblog.com/Manuals/Pear/pecl.paradox.html
Some form of abstraction, to get away from native database methods would probably be advisable. On a Windows machine it would be fairly simple to establish an ODBC connection to the DB and then use the PHP 'odbc_' connectivity functions. This is possible (although less simple) on Unix, too, of course.
That's my 2pence on the avenues you could explore.
Take it easy,
Dan