How can I create a nice invoice, drawing totals from separate spreadsheets?

I have several spreadsheets and want to create a nice looking invoice template in Writer (or Calc) that can take it’s values from individual cells in other spreadsheets.

I’ve read this: http://forum.openoffice.org/en/forum/viewtopic.php?f=75&t=3294 and it seems the only way to directly reference a cell is with the likes of this:
=‘file:///path/name.xls’#$SheetX.$A$1

Is there an easier/GUI way to reference the cell of a local .ods file and how can I feed that to a Writer file?

I’ve tried: Table → Formula, and entering: ‘file:///Users/jarlathreidy/Ja.xlsx’#$Sheet1.$E$3
But it just says, Expression is faulty

I think the instructions here will give you what you want. You basically just need to Edit > Paste Special… > DDE Link and then format the display of the linked entry.

Thank you, that’s exactly what I was looking for! God, I’ve spent so much time, thanks very much.