Before running the update, display error_reporting on high level.
1. Update Joomla itself from 2.5 to 3.0
2. backup your oscommerce and personal dir in front and admin.
3. Just install the 2 zip-files MarvikShop 3.0 into joomla 3.0 to activate the program
* notice in the pull down menu of the adminsite \\\"component not found\\\"
4. second overwrite all the files (admin and front) with a ftp client, Database is 2.5 with your old input.
5. edit the index files (admin and front)
* notice some errors below on the adminsite.
Notice: Constant already defined in /var/www/vhosts/wereldstenen.nl/subdomains/demo/administrator/components/com_oscommerce/includes/application_top.php on line 73
6. Solved by removing configuration table and configuration group table in phpMyAdmin and install the new tables, which includes in the language files.
Notice: Constant __COMPILER_HALT_OFFSET__ already defined in .../administrator/components/com_oscommerce/oscommerce.php(1) : eval()\\\'d code on line 30
7.Forget that one, not important.
Although it cannot happen in a single file, it can happen when including two files containing an __halt_compiler() directive.
8. Copy your personaltemplate files from template/joomlastyle into template/userstyle and set userstyle as default in the back(admin).
9. Update the database in phpMyAdmin with the file attached