Project Line Counter is super handy, but it hasn't been updated since Visual Studio 2005. Here's how to get it to work in Visual Studio 2010…
I'm using PLC in Visual Studio 2010 SP1 on Windows 7 64-bit, but it also worked pre-SP1.
Get PLC from here: http://www.wndtabs.com/downloads/PLC221.zip
Unzip, then install SetupPLC221.exe, you don't need to install Workspace Whiz.
Get PLCReg.reg which has new registry keys for PLC which work with Visual Studio 2010.
If PLC isn't installed in C:\Program Files (x86)\LineCount you will need to edit PLCReg.reg with Windows Notepad to modify the paths.
If you are running 32-bit Windows, you will need to edit PLCReg.reg to modify the registry location [HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Microsoft\VisualStudio\10.0\Addins\LineCount]. I think it should be [HKEY_LOCAL_MACHINE\Software\Microsoft\VisualStudio\10.0\Addins\LineCount] but I don't have a 32-bit machine to test that on.
Double click PLCReg.reg to put the new entries into the registry. You might want to backup your registry first just in case.
Next time you start Visual Studio, you should find the Project Line Counter toolbar in the toolbars when it starts up.