How can I tell if I have Service Pack 1 for Visual Studio 2010 installed?

RTMRel is the "release to manufacturing" release. This is when the product is officially launched. If you have SP1 installed, it would say "SP1Rel" after the version (in the case of Visual Studio).

When you have SP1 installed you'll see instead:

Microsoft Visual Studio 2010
Version 10.0.40219.1 SP1Rel
Microsoft .NET Framework
Version 4.0.30319 SP1Rel

Therefore you are still on RTM (release to market) version, not the SP.