ABB Controller 450 communication with a PC
Theres a few ways to do this. The "best" solution depends on your requirements....
Use a Modbus serial link on the AC450 and a Modbus to OPC link from somebody like Kepware on the PC side. http://www.kepware.com/Spec_Sheets/Modbus_ASCII_Serial.asp
Use ABB's 800xA system as an OPC server only ( ask your local ABB organisation for a single node system with ZERO tags and AC400 connectivity )
Use Novotek's OPC server for MB300 http://www.masterbus300.com/
Upgrade your Advant OS to 800xA
I don't know of any implementations of the EXCOM protocol currently available on Win7, but if you feel like writing an EXCOM driver you could probably do this as well.