Welcome aboard, Ewses!
From your other posts, it looks like you are using TRS 2006. You must have used the CMP to do your downloading, which means that it should have searched the DLS for all dependencies before downloading. Some dependencies may have been missing from the DLs, in which case you should have seen some question marks over in the download helper window.
Did you commit your new engines? If not, open the CMP and then click on the launch button in the tool bar at the top. Uncommitted assets will be committed, and, if there are no critical dependencies missing, your engines should be available for your use after TRS opens.
You can set the CMP to automatically commit downloads from the DLS - In the CMP file menu, open Settings, then select the Miscellaneous tab, then put a dot in the radio button for Automatically commit (on the right side of the dialog). 3rd party stuff will not be automatically committed, so you can do as above or you can select a group items in the main CMP window and hit ctrl-m.
If you truly are missing some critical dependencies -- well, it's a common problem, and there are a lot of threads and posts about how to look for them.
Good luck!
Dick