There are 2 levels of PC DVD region protection: RPC-2 (hardware) and RPC-1 (software). Both need to be worked around in order to play DVDs from all regions. You can check if your DVD drive is region locked (RPC-2) using Drive Region Info. All recent DVD drives will have RPC-2.
The RPC-2 protection in the DVD drive can be removed by flashing the DVD drive with region free firmware. Firmware for most drives can be found at http://rpc1.org.
After this the RPC-1 protection in Windows and the DVD player software can be removed using software such as:
Many standalone DVD players can be made region free by entering codes via the remote control.
Try these: