[funkydunk]

Yeah - the file to edit is modules/Upselling_products/related_products.php

Look for a line that is:

$product_links = func_query($search_query = "select DISTINCT $sql_tbl[products].*, $sql_tbl[categories].category, $sql_tbl[pricing].price from $sql_tbl[products], $sql_tbl[pricing], $sql_tbl[categories], $sql_tbl[product_links] where ($sql_tbl[pricing].membership='') and ($sql_tbl[pricing].productid=$sql_tbl[products].productid) and ($sql_tbl[pricing].quantity=1) and ($sql_tbl[products].categoryid=$sql_tbl[categories].categoryid) and $sql_tbl[products].forsale='Y' and ($sql_tbl[products].productid=$sql_tbl[product_links].productid2) and ($sql_tbl[product_links].productid1='$productid') ORDER BY $sql_tbl[products].product");

The thing to change is the last part - if you want to change it, change to "table_name.field_name" eg:
to order by the orderby setting in the cart admin:

ORDER BY $sql_tbl[products].orderby