As you may know, I have iODBC support in PHP, and it has been patched into GDAL in the GIS Libs, and it’s possible to do the same for GRASS.
I found an inexpensive iODBC standalone driver for MS Access (direct from the MDB file) at Actual Technologies. They also have drivers for Oracle (another one of interest to GDAL/GIS users), Sybase, SQL Server, Openbase, MySQL and PostgreSQL.
Time to grab some MDBs from Arc and try out the GDAL personal geodatabase format driver!