ODBC System DSN:
DBTest - points to DBTest.mdb (Access 2000) using Microsoft Access driver (*.mdb) for Access 2000. No username, no password, no "exclusive" access checked!

TestFile.php content
<?php
    $conn = odbc_connect("DBTest", "", "") or die("Connecting error!");
    $rsRecords = odbc_exec($conn, "SELECT * FROM Table1") or die("Query error!");

    while (odbc_fetch_into($rsRecords, &$row)){
        echo $row[0]." ".$row[1]."<BR>";
    }
?>
Result (running IIS 5.0):
"Warning: SQL error: [Microsoft][ODBC Microsoft Access Driver] The Microsoft Jet database engine cannot open the file '(unknown)'. It is already opened exclusively by another user, or you need permission to view its data., SQL
state S1000 in SQLConnect in C:\inetpub\wwwroot\directory\Test.php on line 3
Connecting error!"

I stopped IIS and started Apache (on the same server and port). Then the connection was established perfectly fine and the result was the content of Table1:
1 Text1
2 Text2
3 Text3
4 Text4