Timepost is a project timer that automatically downloads projects and to-dos from Basecamp. Previously available only for Mac OS X, it is now available for Windows too.
"Using Timepost with Basecamp" offers more details:
Basecamp is one of the most popular project collaboration tools on the market, and makes a great companion for Timepost. You can collect timesheets from contractors anywhere in the world using Timepost, and analyze the report information from your Basecamp account.