No installation is required, and the new feature is easily accessible in a chat window, simply open the "Actions" menu and click "Send a file." Once an item has been selected, the recipient will have an opportunity to accept or decline the transfer.
Google also said that it plans to bring the same functionality to Gmail's integrated chat feature. Considering the fact the Google Talk desktop application has this capability, and since the web-based application has video and voice chat, the ability to send files is a strange omission.
The company hasn't given an exact timeframe for when the feature will appear in Gmail.