Sparkling New Processor installed - Now what?

Hello all,
I have an 2005 SQL server running on Windows 2003 servicing 300 clients. The SQL server now has 2 3.8 GHZ dual core processors and 4 GB of ram with 1 gb network card. Over the past 6 months or so I've noticed the performance start to go downhill. I watched the processor utilization and noticed the server is pretty much getting pegged at about 50% utilization. I asked out network guy and he said a second processor would help with the workload. Guess what? I bought the processor and it doesn't seem to help that much. Does anyone know if special commands need to be run in SQL 2005 to turn the second processor on? What could I be missing?
thanks
KR

<p>You should see 4 CPU (CPU0, CPU1, CPU2, CPU3) in this Processor section of SQL Properties.<br>Do you see 4 of them?</p><p><img src="http://img152.imageshack.us/img152/5105/processorsqo2.gif" title="Processor" alt="Processor" mce_src="http://img152.imageshack.us/img152/5105/processorsqo2.gif" height="632" width="704"><br>&nbsp;</p>

Are you sure your bottleneck is purely processor? What about disk? I/O is normally the first thing to start causing performance degradation. Check your disk counters, queueing, I/O throughput. Check your buffer cache hit ratio and other memory counters to see if you have enough RAM.