I have a Yaesu FT100D tranceiver with a USB CAT control cable to the PC that interfaces with my radio. The CAT control cable allows me to read and control the frequency and mode of the radio using software like HamRadioDeluxe (HRD 5.0), MultiPSK, MixW, HamScope. I also have a SignaLink USB interface which contains its own soundcard altho I had been using my computer's built-in sound card with a home-brew interface before I got the SignaLink.
My first experience with controlling the PC connected to my FT100D was with "LogMeIn.com" on my Windows PC. They have a free version as well as a pro-version ($$) which will control any PC remotely. Your PC must allow remote access.
To turn on remote access in Windows XP, click on START, then right click on MY COMPUTER, then PROPERTIES, then the ADVANCED tab, then put a check in the box next to "Allow Remote Assistance invitations to be sent from this computer". This will allow the ADVANCED button below it to be selected. Press the ADVANCED button, then put a check in the box next to "Allow this computer to be controlled remotely". Press OK, then APPLY, then OK. (For Win7 users, go to START, then right click on COMPUTER, then PROPERTIES. In the upper left area of the SYSTEM screen, click on REMOTE SETTINGS, etc.)
The free version of LogMeIn will not give you audio, but this is not a problem for digital keyboard communication modes. One nice feature of LogMeIn is that it is possible to actually turn on your host machine remotely IF it is WIRED to the internet (not wireless). To enable this feature you must be able to go into the BIOS of your computer and set it to "WAKE ON LAN".
Another program I use is TEAMVIEWER. It has a Voice Over Internet Protocal (VOIP) so that I can hear the audio from my host machine over the speaker of my remote machine. The audio is not good quality and there are a lot of hesitations in it, but it is free.
I hope to get going with a parallel port control of an antenna switch, and a relay to turn off and on the radio.