Extra using statements will very rarely cause problems, and when they do they will be because you have introduced an ambiguous name into the scope (for example, using two namespaces with both define a Vector type, and then trying to write Vector myVector = new Vector() will be ambiguous). The compiler will tell you of these name clashes, and fail to compile your code.
If you run afoul of this, you can either fully-qualify the name reference (MyNamespace.Vector verus SomeOtherNamespace.Vector) or remove the unused using directives.
Note that if you are using Visual Studio, there is an option in the right-click menu while in the text editor for a source file to "remove unused usings." You can also have them sorted via a similar menu command.
using Microsoft.XNA.Framework.GraphicsI can safely assume it handles some sprite graphics and could possibly do some drawing. [continued] – Jonathan Hobbs Oct 5 '11 at 0:01using Microsoft.XNA.Framework.AudioI'll be a bit confused. I might be about to read some bad code, or I can no longer rely on theusingstatements to tell me what goes on in this code file. It might not even handle graphics. I just don't know anymore. This once useful readability tool now cannot be used. – Jonathan Hobbs Oct 5 '11 at 0:03general programming questions more likely belong on Stack Overflow instead of here– Joe Oct 5 '11 at 2:21