QuarkXPress 8.12 provides better ways of importing Charts to be able to print them at High Resolution. Please follow these steps:
1. Draw a picture box.
2.Open the import dialog (Ctrl+E).
3. Select the MS Excel file that contains the chart you want to import.
4. There will be dropdown at the end of the dialog box that shows all the charts present in the Excel File. Select the chart you need and press OK.
Now you should have a Chart that can be printed at High Resolution.
This chart is also linked to the original excel file and the modifications can be updated from Utilities -> Usage -> Picture (Just like any other picture file).
Please post if you still face issues with this.