Jiabao,
Upon bom insert, there is a property called Table Template.
If you browse out for a different template, Solidworks (v?)
supplies a bom-weight and bom-materials among others.
If you only need to add a column to you bill, right click on the top of a column and add. The entered text can be saved, but not updated.
Try the Table Template first and proceed.
I am sure there is alot more help here than I offer.
I have used the bom-materials for weldment assem's.
Happy boming
dsgnr1
Experience is a dear teacher, and only fools will learn from no other.
Ben Franklin
In addition to adding the columns to the table, you will need to add the property to the part/assembly. In the part file, go to file>properties>custom properties and start adding whatever you would like in the BOM (cost, material). When you add the material property, you will need to link it to the material you selected in the material manager (SW 2004 and later). When you get back to the drawing and BOM, you will need to select the new column that you added and tell it to show the custom properties that were created in the individaul parts.