For one of my clients I recently completed a leave form component. Sadly we could not use Infopath as neither the client was consistently installed across the organisation nor did they have an enterprise license. In my research around this topic I did come across a great 7 part article series showing step by step how to create a Leave Form using Infopath. The articles describe all steps in quite some detail and will get anybody going in no time. Once special gem in his series explains how to set the value of a text field to the full name of the currently logged in user using SharePoint Webservices.
the other articles in the series can be found here (note that they are all over the place)