Are you trying to make it look like this? (where X is the checkbox)
Obviously using right text align in the checkbox control only puts the text on the right versus the left, so that's why I am assuming you are trying to do something more complicated.
The only way I can figure you could do this is to break up the checkbox and it's label. Have a checkbox control with no label, then a label control by itself. Put each in a cell in a table inside the data grid cell and properly align the two cells to suit your needs. Set the table to be 100% width so all the cells align left and right against the inside edge of their parent data grid cell.
<table width="100%" border="0"><tr>
<asp:CheckBox Runat="server" ID="chkMyCheckBox" />
<asp:Label Runat="server" ID="lblMyCheckBoxLabel" />