Simon, as Michael stated, the current version of the JS API is 3.9. Version 2.X is currently a mature product, and will no longer be supported as of June 1, 2014. I would highly suggest migrating to version 3.9.
Brad
v2.8 only supports Internet Explorer 7-9. Unfortunately, there is no matrix for version and browser support. In the future, you can go to this link to find the SDK version you are interested in. Download the SDK and go through the extracted folder to the jshelp folder (\arcgis_js_api\sdk\help\jshelp). Supported browsers can be found at the top of the page.
Best,
Brad