<p>Does anyone know how SQL Server determines the order triggers (of same type, i.e. before triggers) are executed.  And is there any way of changing this so that I can specify the order I want.  If not, why not.</p>

<p>Thanks.</p>

The order is set by sql server, the only thing you can do is use a system sp (sp_settriggerorder) to set which trigger will fire first and which will fire last.
Beyond setting the first and last triggers to fire, you can't modify or tell which order sql server will use.  Therefore you will want to build your triggers so they do not rely on which order they are fired.  Even if you determine the order they fire in today, it may change tomorrow.
This information is based on Sql Server 2000, however I do not believe 2005/2008 act differently in this regard.