Did you overload the server or the database? Those are two different issues.
Autosave does save "versions" of your blog posts, but not necessarily individual post entries. That doesn't overload a database. What overloads it is when it is over worked, such as something hitting the database too frequently and too much.
First, find out what their database limits are. Then go through and disabled all of your Plugins one by one to see if they are causing the problem. If they are not changing the impact on the database, and you have updated all of them to work with WordPress 2.7, and you've done nothing else in your Theme or code to tweak WordPress, then it could be that their limits are just too low for your site's needs.