For admin purposes, you can start wizard through Enterprise Manager (right click on any table -> Export data) or by running dtswiz.exe.
Programmatically: with DTS API. You may check forum961, though calling from PHP presents some extra problems.
By using PHP only: use mssql_*() functions to retrieve data and dbase_*() functions to save target dBase file.
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Math problems? Call 0800-[(10x)(13i)^2]-[sin(xy)/2.362x]