Controlling Z-Wave via a computer

You would need something like Homeseer that supports the Z-wave USB adpater and a compatible USB IR receiver. I use a USB-UIRT to receive the IR command and Homeseer picks up that IR trigger and issues the Z-wave "event" through the USB adapter.

My remote is just programmed with a bunch of IR codes (I think I used some old VCR number keys) that are mapped to my five Z-wave switches. I have a command for on, off, dim+, and dim- for each dimmer/switch. Then I have commands for all on and off and some scenes. I have all this running on my HTPC which I leave on 24/7. My remote is a URC MX-980 with a MRF-350 that has an IR emitter attached to the USB-UIRT.

As far as I know, EventGhost doesn't have the ability to communicate with the Z-wave adapter.

You might look at:
http://code.google.com/p/open-zwave/
to see if you can use it to work with EventGhost

Otherwise I think the Homeseer is a good option, or if you have an iDevice you can check out what I am using SQ Remote and SQ Blaster from SquareConnect.com and see if maybe they'll support Z-Wave directly in the future. Currently it is used paired with micasaverde.com's Vera that I currently use too for Z-Wave control.