To connect to an Access db, use this informations (ODBC is used) :
$AdoCon.Provider = "MSDASQL"
$AdoCon.Properties("DSN")="ODBC dsn"
$AdoCon.Properties("UID")="userName"
$AdoCon.Properties("PWD")="password"
$AdoCon.Open
The odbc dsn must be defined through the ODBC icon in the windows control panel (in administratives tools for w2k and XP)

I'm not sure this one will work.

For the record locking, all user can update the DB simultaneously, only if they're :
adding a new entry
changing a single entry that won't be changed by another user

In fact, only the record(s) that had to be changed will be locked for write. all other will be available, and the locked one will only be here for read-only purposes