pc-plc

i have many kinds of plcs in the company where i work,AB, westinghouse,national ,... we can connect any plc to pc and reprogram or design the ladder diagram for these machines ,i need help for first step that how can we view the the instrumentation variabels(temp,pressurs,load)from plc in visual on pc so the operator can moniter or change any set point from pc,any example or site that explain it.i hope i can see simple program in visual basic to get data from plc port and view it on pc screen.
thanks

Search Google for:
HMI OPC PLC

Try www.citect.com if you are after a SCADA package, they claim to be able to talk to any PLC.