The Microsoft sql server Express edition doesn't come with the profiler. And when you are doing some performance tuning of your application using the express edition then you need to profile the traffic that is hitting your sql server.
I found one of useful freeware that can do the tracing with sql server express edition.
However, now you have an ability to use express edition for tuning your system.

SQL Server Express Edition Profiler provides the most of functionality standard profiler does, such as choosing events to profile, setting filters, etc.

Profiler for Microsoft SQL Server 2005/2008 Express Edition

Download here

Visit the official website for this profiler


Have fun with tracing now!!!