I don't know much about Delphi, but it seems that Delphi 8 is .NET compliant so maybe you can import Usc.dll and UsbWrapper.dll in to your project the same way you would import any other .NET assembly. Those DLLs take care of the low-level native USB communication and provide a high-level class (Usc) that you can use in your program to talk to the Maestro.
Those DLLs come with the Maestro Control Center, but if you need help using them you should get them from the Pololu USB SDK because it has the source code of Usc.dll and an XML documentation file for UsbWrapper.dll.
We do not specifically support Delphi, and we do not provide the source code of the Maestro Control Center.
If the suggestions above do not work for you, then you should try just using the Maestro's virtual COM port. The Maestro's serial protocol is documented in the Maestro user's guide, and you can search the Internet for something like "serial port delphi" to find information about how to send a receive bytes on a serial port with Delphi. Make sure you read about the the Maestro's Serial Mode setting in the user's guide and configure the Maestro to be in the right Serial Mode (most likely USB Dual Port).