Why do you say by a sub-domain.
Normally, create a sub-domain is generally free and just require a configuration of your hosting server.
Normally, also for a sub-domain, your hosting server control panel should give you the possibility to give a specific directory.
Which hosting server are you using ?
See the FAQ
www.jms2win.com/faq that provide you a list of help depending on some hosting server.
Start to configure your hosting server with your sub-domain and also decide in which directory where you want to locate it on your disk.
If you choose the sub-directory /guildwars, this will give you the possibility to define the domain ans you have already do it in JMS.
For the moment, I suspect that the /guildwars does not exists (you have not replied to this question). This directory may be created by your hosting server when you will define the sub-domain or you will have to create it manully before asking JMS to deploy the slave site into this sub-directory.