The Active Directory Schema Microsoft Management Console (MMC) snap-in is not available by default in the list of snap-ins. You must first register schmmgmt.dll and then you can create a console that includes the Active Directory Schema snap-in.
If you've already registered schmmgmt.dll and built an Active Directory Schema console, you can skip this section. If you don't know what I'm talking about, follow along here. You can't hurt anything by doing this again, even if it was already done at some point.
To register the console, click Start, Run and type regsvr32 schmmgmt.dll in the dialog box. You'll receive confirmation that the registration succeeded (see Figure 2).
Figure 2 Registering schmmgmt.dll.
After you've registered schmmgmt.dll, you can create the MMC console with the Active Directory Schema snap-in. Follow these steps:
Open the Run menu again (click Start, Run).
Type MMC and press Enter. Console1 opens.
From the File menu, select Add/Remove Snap-in. The Add/Remove Snap-in dialog box opens.
Click Add. The Add Standalone Snap-in dialog box appears. The Active Directory Schema should now be available as a snap-in, as shown in Figure 3. Select it and click Add.
Click Close to close the Add/Remove Standalone Snap-in dialog box. Click OK in the Add/Remove Snap-in dialog box. You should now see the Active Directory Schema snap-in in the Console1 MMC.
Choose File, Save As. The Save As dialog box opens. In the file name box, type Schema.msc. In the Save in box, select Desktop. Click Save. This saves a Schema console on the desktop.
Figure 3 Selecting and adding the Active Directory Schema snap-in.