kobra:
You were not as specific in your first posting
And I was confused when you stated that you clicked configuration which would indicate the admin section...
go to
admin > tools > defines page editor > select "define_shopping_cart.php" from the drop down > edit away
OK, now I'm confused...
In the Admin screen, I went to "Tools" and found "Define Pages Editor". I see the following list:
http://www.orcatools.com/pgEdit.jpg
I see no "define_shopping_cart.php" in that list.
I also went to the windows explorer & did a search for "define_shopping_cart.php", but no such file was found.
In the Admin screen, if I click on "configuration", I get:
# Configuration
* My Store
* Minimum Values
* Maximum Values
* Images
* Customer Details
* Shipping/Packaging
* Product Listing
* Stock
* Logging
* E-Mail Options
* Attribute Settings
* GZip Compression
* Sessions
* Regulations
* GV Coupons
* Credit Cards
* Product Info
* Layout Settings
* Website Maintenance
* New Listing
* Featured Listing
* All Listing
* Index Listing
* Define Page Status
* EZ-Pages Settings
# Catalog
* Categories/Products
* Product Types
* Products Price Manager
* Option Name Manager
* Option Value Manager
* Attributes Controller
* Downloads Manager
* Option Name Sorter
* Option Value Sorter
* Manufacturers
* Reviews
* Specials
* Featured Products
* SaleMaker
* Products Expected
# Modules
* Payment
* Shipping
* Order Total
# Customers
* Customers
* Orders
* Group Pricing
* PayPal IPN
# Locations / Taxes
* Countries
* Zones
* Zones Definitions
* Tax Classes
* Tax Rates
# Localization
* Currencies
* Languages
* Orders Status
# Reports
* Products Viewed
* Products Purchased
* Customer Orders-Total
* Products Low Stock
* Customers Referral
# Tools
* Template Selection
* Layout Boxes Controller
* Banner Manager
* Send Email
* Newsletter and Product Notifications Manager
* Server/Version Info
* Who's Online
* Admin Settings
* Email Welcome
* Store Manager
* Developers Tool Kit
* EZ-Pages
* Define Pages Editor
* Install SQL Patches
# Gift Certificate/Coupons
* Coupon Admin
* Gift Certificates Queue
* Mail Gift Certificate
* Gift Certificates sent
# Extras
* Record Artists
* Record Companies
* Music Genre
* Media Manager
* Media Types
Here is the symbol I am talking about: 
And this is my shopping cart screen from my site:
http://www.orcatools.com/cartpg.jpg
So, are we on the same page here?