Ok guys, thank you for the advices.
I couldn't figure out how to put the main domain name in a directory without it to appear in the adress bar so I just left it like it in the root, but site2.com works fine now.
Thanks again.

(yeah, it's a long way til' the top if you wanna rock'n'roll)

I couldn't figure out how to put the main domain name in a directory without it to appear in the adress bar

I think you are not only overcomplicating but you might also over confusing yourself…:-)

It is really this simple and your host for sure has a domain management tool for it:
www.site1.com -> site1 folder
www.site2.com -> site2 folder

You're right but it gives me :
http://www.site1.com/site1 folder instead of http://www.site1.com/

Thank you anyway.

Then something is not set right like an redirection in a htaccess file. Again, either you do it via htaccess OR your webhost settings.

Hi guys,
I've read many things on this forum and others and tried many things too these days about that, but I still got a problem.

With this .htaccess on the root folder :
`
RewriteEngine On
RewriteRule ^$ zpdirectory/
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ zpdirectory/$1
`
The ZPdirectory doesn't appear in the URL when I type www.mysite1.com but it still appears in the URL navigating through albums and images.
I've updated to Zenphoto 1.4.5.7.
I've re-run setup, refreshed the database, cleaned the html cache, even tried some exoctic stuffs with zenphoto.cfg.php but the subfolder still appears in the URL.
Did I really miss something in order to hide that damned subfolder in the URL ?
Do I have to change something manually in the parameters, in the root .htaccess or in the /ZPdirectory/ .htaccess ?

Again, if you don't want to have the folder ZP is installed in in the URL redirect the domain to the folder so the folder becomes the root. Either do that via your host's server config backend or on the root htaccess. As long as that is not done, you will get the folder in the url because that is the path.

There are loads of instructions like
http://webdesign.about.com/od/mod_rewrite/qt/site_redirects.htm

There is really ONLY one way to do what you want. You MUST have a domain that points directly to the ZP install folder. Anything else simply does not work.

Rewrite rules simply change links, so you could have a rule in domain1 that redirects to domain2. Or you can have a link that redirects domain1 to domain1/folder. Neither of these is what you are asking for.

So, contact your host and find out how to setup "subdomains" for your site. If you have a reasonable hoster that will be quite simple and allow you to have things like:

www.sbillard.org
testalbum.sbillard.org
testalbum-2.sbillard.org

that all point to "root level" Zenphoto installs.

I will mention again that I do not understand why you are so unwilling to follow our advice. But rest assured, this is the end of this discussion.