The AJAX interface provides your web applications with JavaScript based access to translation services.

The SOAP interface provides a strongly typed, web service standards based programming model supporting rich development environments such as the .NET framework.

The HTTP interface provides a high degree of interoperability for any network enabled application and supports a broad range of development environments.

Comprehensive reference for Microsoft Translator APIs on MSDN.

Windows Azure Marketplace gives you a convenient way to sign up for the Microsoft Translator API. The set of offers includes an option for FREE use of the API. You can try out the functionality of the Translator API without having to write any code, right there on the Windows Azure Marketplace.