Heck, you don't get a full blown version of anything on the PPC, not even .NET.

I'm not sure how easy or difficult this would be, but I would try getting around your issues with a datagrid. After all, you can make a datagrid look pretty similar to a spreadsheet, and nothing is going to look all that much like a desktop system anyways. You could use this to enter data into cells, then move that database into a SQLCE database, then export it via XML to a desktop. I believe you can move XML into Excel, though I have never done it.

Entering data into a spreadsheet on a PDA is painful. I use a technique similar to what I describe above, except that when the user clicks on a cell, they are taken to a form specific for entering the data in that cell (or more than one cell at a time). This all stores in a DB, and I don't deal with Excel, but the same sort of technique might be worth exploring for your needs. That would give you all the functionality of the .NET CF, rather than just pocket Excel, which will be painful anyways.