For osCommerce (going through the steps now, but my host just crashed...)
1. Log in to your host (I use hostmonster, but I've heard gootd things of 1&1 as well). Create a blank database via your web hosting control panel (or use a remote GUI or terminal... whatever suits your fancy)
2. Download the osCommerce zip file from the downloads section of
osCommerce, Open Source Online Shop E-Commerce Solutions, unzip it and extract the 'catalog' folder.
3. If you want your shop to be available at
http://www.yourdomain.com/catalog then upload the whole of the catalog folder to the root directory of your website via FTP. If you want the site to be available at
http://www.yourdomain.com then just upload all of the contents of the catalog folder, but not the folder itself.
4. Make sure that the permissions on all of the folders are set to 755, and if that does not work then set them to 777. Make sure that the includes/configure.php file and the admin/includes/configure.php file are set to 777 for the duration of the install. Once the install is complete reset to 644, 444, or 400 depending on your server setup.
5. Then go to
http://www.yourdomain.com/install and begin the install procedure. Your DB Server will probably be 'localhost', your db user name and password (for mysql access) will have been provided to you by your web hosting company. The name of the database you already know - because you just set it up. Do not enable SSL, select to store sessions in the database and not files (untick the box), and do not enable persistent connections.
6. After the install create a folder called 'backups' inside the 'admin' folder (via FTP), and delete the install folder. Reset permissions on the two configure.php files.
7. Password Protect your 'admin' folder using the Password Protect feature in your web hosting control panel (or manually edit the .htacess file if that suits your fancy).
M.
EDIT: Full instructions here btw:
http://www.oscommerce.info/kb/osCommerce/Installation_and_Upgrades/41
To upload via FTP you can try FileZilla, it's free and fairly good...