Yup, that's a problem with the TCP/IP stack software itself.
Some hardware/driver installations seem to offer less waiting on the part of the CPU, while it listens for a packet that it is expecting but has not arrived.
Others quite dramatically freeze up the system while waiting for a packet.
All of this is outside the simulator itself and represents yet ( another ) problem with DX9.0 & directplay.
I've sometimes been able to ameliorate the issue by completely uninstalling the network card interface drivers, rebooting and then letting Windows install the latest drivers available... preferably the WHQL ones.