I want to first start off by saying creative laboratory's drivers and corporate policies leave much to be desired.

When I installed the creative drivers on my vista 64, I had only installed the minimum, which also, if I remember correctly gives you the greatest performance.
I was having many driver issues which were resulting in blue screens of death. I have uninstalled and reinstalled many of my drivers. In the process of doing so, I had stumbled upon a way to enable EAX in windows vista 64.
I'd do not guarantee that this will work for you, it is working for me. I will step you through the process, that should enable it for you. I am running windows vista ultimate 64 bit.
Boot the machine to safe mode by pressing F8 as the computer is booting. Uninstall the creative laboratories drivers. Next insert the CD that came with the card and load all options for the drivers. In other words the full install. Reboot your machine.
After doing this your microphone settings will need to be a reconfigured, and some of the creative gui's will no longer function. Now you should have a creative folder in your start menu. Next open the creative alchemy (x-fi edition) add guild wars, then open audio console launcher. There should be a tab labeled EAX. At this point simply enable it. You'll also see many other features have been separated into their own programs.The THX console has the base boost.
Now when you open guild wars and select options > sound you should be able to add the checkmark to the EAX box and the 3D audio effects box. It may take some time to go through all the individual programs without the aid of the GUI to make the appropriate adjustments. If you have any questions feel free to post them here.The reason I posted this is because I had struggled with this and have been asked in messages for this information.