Hy ! I'm french (sorry for my english)
Before install JMS on a final website, i'want to test it on a webdev site, and i'v install a J-1.5.9 in a sub folder (www.mydomain.com/jmultisites) and when i'want create a slive site, i've test lot of url param :
slive name : demo
- www.mydomain.com/jmultisites/demo
- www.mydomain.com/demo.jmultisites
- demo.jmultisites.mydomain.com
for exemple, but that not ok !!!

if i've give the same directory www.mydomain.com/jmultisites

www.mydomain.com/jmultisites, evidence, the J-install taking hand, and i can't use mys master website...
then, it is possible to use in a site installing in a sub folder, or it's necessary to install it in a real website with only www.ydomain.com
thank's

To use JMS, in a sub-directory, you need to work on a unix machine and have symbolic avaialble.
If this is the case, you have to specify the deploy directory to allow JMS create the symbolic links that are used to redirect all the queries to the master directory.
You also have to check that your apache or .htaccess file is configure with option followSymLink to follow the links.

On Windows IIS, you have to use Virtual Directory to redirect them to the master directory.