If you’re building a text service DLL, you almost certainly don’t want to use Visual Studio 2008’s compiler. The problem is that Visual Studio 2008 uses a new C Runtime Library, and if you build your text service with Visual Studio, your text service likely won’t load in all applications. (Plus, you would have to redistribute the C Runtime Library.)
What to do instead?
Well, I would recommend installing the Vista (or XP) DDK and use the DDKWizard instead. The DDK comes with its own C/C++ compiler that uses the C Runtime Library that ships with the OS (and won’t cause problems with other applications), and the DDKWizard will let you use all of Visual Studio’s awesome capabilities.