Hi there, here's how you go about doing that.
Open up skin1/customer/main/products_t.tpl
this file does have the code needed for a buy it now button, they have just coded it out. If you hvaen't changed the file yet then it will start at line 62, just remove that line and line 66 and you should be good to go.
This is what those 2 lines look like in case you have changed that file, these are what you have to remove.
Code:
{*** Uncomment it if you need 'Buy Now' button ***
Code:
*** Uncomment it if you need 'Buy Now' button ***}
Hope that helps
Rob