If I remember correctly, the DGC components have pretty much died out in recent times, since they weren't updated for ages (correct me, people, if this is wrong).

I think that your best bet would be to use a more recent component set. There are a few around, though I'd guess that none encapsulate things in exactly the same way.

See if Powerdraw, DelphiX or the Omega Project.

If you can list some errors, it may be possible to update the headers for later versions and recompile everything (assuming it comes with source - is that the case?). Tell me where to grab that copy of DGC and I'll see if I can recompile it for D5/6 (in a few hours time, that is).