Haven't completely tested if but should be something like this:
Select tblComputers.Computername, tblComputers.ComputerUnique, temptbl.Regkey,
temptbl.Valuename
From (Select tblComputers.Computername, tblComputers.ComputerUnique,
tblRegistry.Regkey, tblRegistry.Valuename, tblRegistry.Value
From tblComputers Inner Join
tblRegistry On tblComputers.Computername = tblRegistry.Computername
Where tblRegistry.Regkey Like '%windowsupdate%') temptbl Right Join
tblComputers On tblComputers.Computername = temptbl.Computername