Sure,
Depending on what ODBC driver manager you use, you will have slightly different setups, but basically an odbc.ini file will contain your DSN, a putenv("ODBCINI=/path/to/odbc.ini"); in your script will locate it for php.
You will need to compile the ODBC layer in, which basically just binds the Driver Manager to PHP, so you still need a driver.
There is a HOWTO on ODBC-PHP at www.iodbc.org that goes into this in some depth.
Hope this helps!
Best regards,
Andrew
Andrew Hill
Director Technology Evangelism
OpenLink Software
http://www.openlinksw.com
XML & E-Business Infrastructure Technology Provider