As others have posted, adding a PC to the automation will probably make your setup more flexible. If I were a purist, I would prefer the lot to be in an embedded system however there is really nothing on the market being embedded that can offer the flexibility of many Windows HA systems.
So if you leave your Alarm as an embedded system, you've got a much higher chance of the thing not falling over when you most need it. A number have posted about the virtues of the ELK system and having people like Spanky in the forum. The ELK is pretty good and the Serial Protocol allows for a lot of flexibility in managing it from a HA system. The ELK has some quirks but I'm sure most others have them too. Personally I would vouch for the ELK, the architecture makes sense, its very flexible from an Alarm point of view while still being reasonably feature rich in the Automation side.
If you're looking to integrate all different sorts of technology like 1-wire, rf ground loops, house music, callerid on screen, touch screens (outside of the ELK touch screen) then you should seriously think about adding a PC Based HA sollution. I've paired an ELK with Homeseer which has offered a damm good platform to plug things into.
ELK: has 40 points of monitoring, controls X10 lighting, TR40 Thermostat and manages contact lighting and pool equipment out the back. It sends and receives information via the Ethernet expander.
Homeseer: House lighting, Music, Touchscreen, 1-Wire Temperature, Bluetooth interface, GSM SMS Engine, House Speech Announcements, Event Management. The event management (rule builder) is extremely flexible and relatively easy to use.
I hope this post hasnt gone too far off thread however I've wanted to show that by combining the best of both, you can build something extremely powerfull. My latest addition is a Roomba Vacuum cleaner and I've added a Bluetooth receiver to it. I can schedule Homeseer to send the robot out and vacuum and come home whenever I want. To the point, I can create events that can be activated by my ELK Keypad, Web Page, MSN Messenger and Touchscreen that can send it on a cleaning mission
Cheers 4 now

Pete