Welcome to X-Cart! Please start by reading the forum rules, and posting your X-Cart version in your signature (Edit profile, enter version, enter password, save):
http://forum.x-cart.com/viewtopic.php?t=6489
Next, try the manual, found here:
http://www.x-cart.com/manuals.html
If you still have questions after reading the manual, please search the forum first, as many of the most common questions have been answered multiple times. You need to make sure to use 'and' in your searches. For example, 'welcome and text and remove' will get you the result you want.
As for the white line, do you mean the space between the vertical menus and the edge of the browser? That is a table cell in customer/home.tpl.
A tip for template editing: try webmaster mode. It will allow you to edit text on the fly, and also let you know which templates are which.