mysql_connect() [function.mysql-connect]: Access denied
* warning: mysql_connect() [function.mysql-connect]: Access denied for user 'nobody'@'localhost' (using password: NO) in /home/a4432462/public_html/drupal/modules/oscommerce/oscommerce.module on line 254.
* warning: mysql_query(): supplied argument is not a valid MySQL-Link resource in /home/a4432462/public_html/drupal/modules/oscommerce/oscommerce.module on line 288.
* warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource in /home/a4432462/public_html/drupal/modules/oscommerce/oscommerce.module on line 289.
* warning: mysql_connect() [function.mysql-connect]: Access denied for user 'nobody'@'localhost' (using password: NO) in /home/a4432462/public_html/drupal/modules/oscommerce/oscommerce.module on line 254.
* warning: mysql_query(): supplied argument is not a valid MySQL-Link resource in /home/a4432462/public_html/drupal/modules/oscommerce/oscommerce.module on line 363.
* warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource in /home/a4432462/public_html/drupal/modules/oscommerce/oscommerce.module on line 364.

Assuming that you already
Assuming that you already have oscommerce configured with its own database, the module must have some settings, probably in Drupal's /settings/oscommerce page, were you must specify the db host, db name, db user and db password for oscommerce.
SQL connection issue
There is no setting under settings. Where can we set the db login information?
Been there... And now I am
Been there... And now I am there again. For some reason, under http://yoursite/admin/settings/oscommerce I am not able to configure my database connections. So, I edited osscomerce.module, around line 245 and so on:
Change 'your***' for your variables and, on http://yoursite/admin/settings/oscommerce, you should at least see "Link to osCommerce database is valid" on the top of your page. From there you may keep on your debugging.