If when you say "CH Serial port" you actually mean "CH Gameport" or "Analog Game port" , then yes a "GOOD" USB Adaptor will work, I have had 2 cheapo Gameport-to-USB Adaptors that gave me problems, but the Radio Shack version of Gameport-to-USB Adaptors ( with the 4 position selector switch ) have never given me problems..... still using one today with CH USB Fiter Stick, CH USB Pro Throttle, CH analog Game port Rudder Pedals runned through the Gameport-to-USB Adaptor...... my OS is windows 7 64 bit.....
also, it shows up as "USB Adaptor" in windows game controllers setup......
the game "Aces High" also picks it up as "USB Adaptor" you just have to map your Rudder Pedals to it ( the Axis )...
hope this helps....