You may want to be careful with direct connections like that between the radio and PC, lot of military radios output a DC Bias voltage for the microphone elements that the PC Audio may not dig, also the coupling between the PC Audio that's intended to be around 10K and the microphone inputs on most military radios are around 600 Ohms. It will work, but the overall frequency response may be weird. And if an impedance miss match exists, it may also interduce hum or other byproducts that will be part of your transmitted signal. 

If you are using RTS or DTR to control transmit, also remember that a lot of the older military radios had larger current drains on the PTT line that will damage that port. 

The biggest deal today is finding modern computers that still have dedicated Audio In and Out ports along with a RS-232 port. Almost everything is now moving to external USB driven interfaces that can provide two-way audio or external RS-232 ports. 

I have been using old Panasonic Toughbook's for some time in the field because they still have audio and serial ports but looking at migrating all field opps over to a Dell Latitude Toughbook running Ubuntu because the old Panasonic running Win 7 is getting a bit long in the tooth so will be evaluating external devices just for that function.

Ray F/KA3EKH