When importing an Excel spreadsheet that contains images or objects in hidden 
cells, the images and objects do not exist in OOo when the cells are unhidden.  
Excel 2003 was used to create the test file.

Steps to replicate:
1. Launch Excel 2003
2. Create a blank worksheet.
3. Highlight cell B1
4. Insert picture via Insert - Picture - From File and select a simple picture
5. Click drag the bottom right corner to resize the image so that it is only 
two cells wide.
6. Lock picture to cell via Format - Picture - Properties and choose "Move and 
size with cells"
7. Highlight column B and C, then right-click on column header and choose "Hide"
8. Highlight cell F1
9. Insert object via Insert - Object - Create From File and select a simple 
Word Document
10. Click drag the bottom right corner to resize the image so that it is only 
two cells wide.
11. Lock object to cell via Format - Object - Properties and choose "Move and 
size with cells"
12. Highlight column F and G, then right-click on the column header and 
choose "Hide"
13. Save Excel document.
14. Close Excel 2003
15. Launch OpenOffice.org
16. Open the Excel document in OOo
17. Highlight column A and D, then show hidden cells via Format - Column - Show
18. Highlight column E and H, then show hidden cells via Format - Column - Show

You will then see that the image and embedded object that were inserted in 
Excel are no longer visible when imported by OOo.  The same image and embedded 
object are normally visible when imported if the cells associated with them are 
not first hidden in Excel.  I've been using OOo 2.4.x so I don't know if the 
bug has been fixed in OOo 3.x