Тоже столкнулся, решил так:
I just resolved this issue, I met the same problem today.

Environment: ubuntu server, MySql 5.1, PHP 5, drupal 7

Previously I created the detail tables in the database by executing the SQL queries, then I met the error "Table variable already exists" during install - that's because the table "variable" was already there.

Then I dropped the database, and re-created a empty database only, then install the drupal 7 from install.php. Everything works fine.

Hope this helps,

Yao