SELECT
Format([dateField],"mmm yyyy") AS MonthYear,
DSum("amountField","yourTableName",
"Format(datefield,'yyyymm') <= '" & Format([dateField],"yyyymm") &
"' And Year(dateField)=" & Year([dateField])) AS RunningTotal
FROM yourTableName
GROUP BY
Format([dateField],"mmm yyyy"),
DSum("amountField","yourTableName","Format(datefield,'yyyymm') <= '" & Format([dateField],"yyyymm") &
"' And Year(dateField)=" & Year([dateField])), Format([datefield],"yyyymm")
ORDER BY Format([datefield],"yyyymm");