BleepingComputer.com: Excel '03: Making Document Un-Saveable

I have an employee expense report I'm trying to fix up.

People are supposed to be able to:
-enter personal info (credited to, etc)
-enter miles driven
-enter costs incurred

I have been able to lock the calculations in the cells that give a grand total for all expenses, as well as calculating mileage (so people don't accidentally put their milage in the wrong box). Those cells are un-editable now.

Now, since everyone in the company access this off the network, I need to prevent people from accidentally saving it. They still need to fill it out, so they can print and submit to their department heads.

I didn't see an option when I was enabling sheet protection to do this. What did I miss?

Sharing a workbook is not simple in Excel. At least in 2000 we've seen some issues.
But there's nothing to stop you from trying.
I would start by clicking the HELP button and typing "share workbook".
Why? so that you can get the entire picture of what is involved. Please read all the helps.
One of the first ones I'd look at is "About worksheet and workbook protection", the latter being what you're after.
Then I'd read "Edit a shared workbook" section as this shows how to place certain restrictions.
Good luck. It'll work after you get all the requirements figured out.

Why not make it read only (on the operating system level) and/or change the permissions to deny modification?

XD, thanks Andrew. Forgot about that! Stupid me.

Further to all this, I would save the original file in your own area as a backup copy, then save the one you want people to work from as a template.

Then if people double click the file, they automatically get a new workbook as a copy rather than opening the file itself.
Downside is if people use file > open to get to it, then they will open then template and their save as... will also be a template (but no real harm in that).

Best option is to talk to your IT sysadmins and put it in a share folder which can be used for workgroup templates (a setting you can fix using group policy). Then people don't have to browse, they just do file > new > pick a file (your expenses template in this case).

You don't mention which version of Excel you and the other staff are using.
If it's 2007 then consider using office button > prepare > mark as final. This will always open as read only from then on. Do the same in reverse to make changes saveable.
If 2000/2003 when you do save as, look at the top right for tools menu > general options > tick the box for "read only". This will remind people they should only open this read only, but that can be annoying as it is another dialog box to get rid of.

Changing attributes to make something read only is usually the simplest way, but be wary if the files get moved around a lot or backed up and restored that this attribute might get lost along the way.