Firstly, the problem is with your Quicksilver. (I am using B54(3815) on Leopard) I suggest, you keep your script out of Quicksilver. Put your calculations in applescript's dialog box and see the results in a dialog box. Use only Quicksilver's triggers to assign a shortcut to the script. Dont use Quicksilver's text pane or actions pane.
Second, what exactly do you want? --the calculator script I wrote will only do + - / * and ^ --the spotlight calculator is more powerful. To script it, read its man page by typing "man math" --I don't know about the "bc" command that you are using
