Just after I said about spreadsheets being used to track Olympic medals I find that Google has been updating Google Doc spreadsheets.
It has added ‘protected ranges’ to the documents, allowing
designated sections of spreadsheets to be locked down to prevent other
users editing the content held there.
This is actually a very useful and necessary feature for Docs users,
as it can be a real pain going back over things when small edits or
erroneous changes are made and need fixing.
From: The Next Web
You can also find A Step Guide to Protected Ranges in Google Spreadsheets which is a slide show which clearly shows you what to do.