Pass the sheet name with the Range parameter of the DoCmd.TransferSpreadsheet Method. See the box titled "Worksheets in the Range Parameter" near the bottom of that page.
This code imports from a sheet named "temp" in a workbook named "temp.xls", and stores the data in a table named "tblFromExcel".
Dim strXls As String
strXls = CurrentProject.Path & Chr(92) & "temp.xls"
DoCmd.TransferSpreadsheet acImport, , "tblFromExcel", _
strXls, True, "temp!"