The character for the string type is 's'. It's undocumented. Also I was mispelling the method OpenCurrentDatabase()
The following code does it works:

$h= OleCreateObject("Access.application.8")
OlePutProperty($h, "Visible", 'b', "true")
OleCallProc($h, "OpenCurrentDatabase", "s", "c:\bd.mdb")
OleCallProc($h, "Run", "s", "MyProc")
OleCallProc($h, "CloseCurrentDatabase")
OleCallProc($h, "Quit")
OleReleaseObject($h)

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Luis Hevia