Try the following:
Select tblComputers.Computer, tblComputersystem.Manufacturer,
tblComputersystem.Model, tblPROCESSOR.Name As Processor,
tblComputers.LastknownIP, tblComputersystem.TotalPhysicalMemory,
tblOperatingsystem.Caption
From tblComputers Inner Join
tblComputersystem On tblComputers.Computername =
tblComputersystem.Computername Inner Join
tblPROCESSOR On tblComputers.Computername = tblPROCESSOR.Computername
Inner Join
tblOperatingsystem On tblComputers.Computername =
tblOperatingsystem.Computername
Where tblPROCESSOR.DeviceID = 'CPU0'