Hi doctorlife
OK, let me get you a small rundown on the installation. There are actually only a few steps necessary you have to follow.
(1) Install a Joomla 1.0.5 or use the update from 1.0.4 to 1.0.5. Important is that you do not use any language/country specific Joomla version you can find on all kind of websites. Please uses the original English version you get at Joomla.org, or use the download from my website.
http://www.mytestground.com/cms/index.php?option=com_remository&Itemid=35&func=select&id=1&lang=en(2) Very important is that you install the two patches you will find for Joomla 1.0.5, because they fix some bugs found in it. The first one is the Frontpage ID patch you find here in the forum, or on my website, and the second one is the SEF patch you will find around this forum here, or on my website. Also, if you are intending to use the Community Builder 1.0 RC2, you will have to get you a Joomla 1.0.4 includes/database.php file and replace the one in your Joomla 1.0.5 installation.
http://www.mytestground.com/cms/index.php?option=com_remository&Itemid=35&func=select&id=6&lang=en(3) Then you just download the Mambelfish 1.5. Just get it from my website, it is a Pack with the component, the module, and the searchbot. Just unpack it and install the component (disregard any error messages), install the module, install the searchbot(don't forget to activate it).
http://www.mytestground.com/cms/index.php?option=com_remository&Itemid=35&func=select&id=1&lang=en(4) After that, you download the Joomla 1.0.5 Mambelfish 1.5 Patched Files, unpack the ZIP and use the files included to replace the ones in your installation. It saves you the time to manually patch the files like described in the PDF in the Mambelfish Pack.
http://www.mytestground.com/cms/index.php?option=com_remository&Itemid=35&func=select&id=6&lang=en(5) Now you can install any additional language, but be sure that they are the new language files which are necessary since Joomla 1.0.4. Further you have to make sure that you activate the languages in the Mambelfish configuration. Important is that you set the ISO Key (en = English, de = German, nl = Dutch, etc) right.
(6) Now you should publish the Mambelfish Module, so that you can switch between languages in the frontend. I would always leave the site language set on the original installation language (English) to avoid problems in the beginning. But there should be actually no problems if you use a fresh clean installation without any content.
Now to the issue of VirtueMart and the Communitybuilder.
You should first of all, after you installed you Joomla and Mambelfish, install the Community Builder and get it up and running. The only issue I know is the one which can be fixed by replacing the Joomla 1.0.5 database.php file with the Joomla 1.0.4 database.php file. The setup of the languages is actually real easy because the Community Builder has a Plugin Manager and you can install the language you need as easy as you install the languages in Joomla. You also need to use the Login Module of the Community Builder and unpublish the one from Joomla.
http://www.mytestground.com/cms/index.php?option=com_remository&Itemid=35&func=select&id=4&lang=enVirtueMart is also not a problem. You can just install it, install the modules you want and of course the searchbot. In the Pack on my website, you also will find a language pack with a lot of common languages in it. Unfortunately you will have to copy the needed language file manually into the VirtueMart, there is no installation tool for it. But there is a language component for VirtueMart, which allows you then to edit the language files through the backend.
http://www.mytestground.com/cms/index.php?option=com_remository&Itemid=35&func=select&id=2&lang=enFurther, you only have to use the one login module for everything. The VirtueMart needs of course a little more information about the user, but it will requested the information once the user makes some purchase.
I hope I did not miss anything here, but if, please feel free to fuss at me so I can correct it ...