There is a plugin for Firefox that can be used for Offline Circulation: https://addons.mozilla.org/en-US/firefox/addon/14399
Once installed there will be an icon for the Offline Circulation Tool in the status bar at the bottom of you Firefox Window.
Additional instructions for using this Plugin can be found on the Koha Wiki: http://wiki.koha-community.org/wiki/Offline_circulation_firefox_plugin
The Offline Circulation Utility can be downloaded at: http://millruntech.com/koha/koha-tools/koha-offline-circulation
The offline circulation tool for Windows will generate a KOC file that you can upload into Koha once your system comes back up.
On the Circulation menu click 'Offline Circulation File (.koc) Uploader'
Browse your computer for the *.koc file
Once the file is uploaded, click the process the file
When this is complete you'll see the summary of actions from when you were offline (including any errors).