First Nirm is right, vm1.5 under heavy development.
ATM it happens often that the market looks useable and one week later even the installer is not working. Atm rick changed the configuration data managment. Before the first RC expect strange problems. But... the problems here seem not really related to vm1.5.
I got the error "There was an error uploading this file to the server." When I use the extension manager to upload com_virtuemart_1.5_nightly.zip.
The most common reason for this problem is that the File you have uploaded is too big.
The File Size Upload Limit on your Server is set too low to allow larger files to be uploaded. By
default PHP allows files up to 2 MB, but you can set to 4 MB to get rid of this error.
If you have access to the php.ini, then change the directive upload_max_filesize to "4M"
and reload the server configuration.
If you are running PHP in CGI mode on Apache, you can place an .htaccess file in your
Joomla! root directory and place the following code inside:
php_value upload_max_filesize 4M
This will solve the problem.
VM1.5 is bigger than needed, because there is a lot of old unused code that will be removed if we clear it up before the release. Maybe we will make the sample files as module to avoid this problem.
I got the following error when I ftp the files to tmp directory and install it from there:
JInstaller::install: There is already a folder called '/xxx/www/administrator/components/com_virtuemart/virtuemart.ini'. Please initially check whether:
• the Extension is already installed
• the file names in the XML file are spelled correctly
• there are no XML files listed inside the extension.xml file
• all of the files (not including XML files) are correctly listed in the extension.xml file and there are no duplicate entries
• there is an empty folder listed from a previous installation attempt
Looks like you had an old installation in your joomla.
P.S. I know this is not the right place to post this but I cannot add a new topin in Virtuemart 1.5

This is okey :-). You are just a signal that it is time to move on and to open some forums for vm1.5 asap.
Cyaas Milbo