Shareen, see post 185 in this thread. It does exactly what you want.
There is a mistake in the notes.. you need to edit {xcart_dir}/skin1/customer/home_main.tpl, not home_main.php (there is no such thing).
Also, see the additional info below....
Also, as many people have noticed, 4.1.x sorts products by the title by default. X-cart has no provisions for sorting by Add Date. The thread at
http://forum.x-cart.com/showthread.php?t=38263 deals with this issue, but if you read the last post I am personally having a conflict with Add_Date and recommended products.