To check if you have SP1 installed, look here:
Visual Studio > Help > About Microsoft Visual Studio
 
If a service pack is not installed, you will get:
RTMRel is the "release to manufacturing" release. This is when the product is officially launched.

 
If you have service pack 1, SP1 installed, it would say "SP1Rel" after the version

 
 
 
For futher information, see here.