The set the default sales conditions, you should use the generic OpenERP tool to set default values for any field.

1. Go to your user menu (top right corner) and click on "About OpenERP".
2. In the about dialog box, click on the top right link "Activate Developer Mode".
3. Then go to the quotation form (create a new quotation).
4. Write your sales conditions in the bottom field
5. Click on the debug selection on the top left corner
6. Select "Default Values"
7. Select "Sales Conditions = ..." in the dialog box
8. Click on the button "Save default values"