The visual redist is a runtime library, a way to share a set of functions among different programs. All programs created using Visual C++ 2005 require it. Redistributable runtimes are mostly installed silently, so you need not be worried about it.
Visual C++ 2008 is the newer version, it'll be required to load programs that were created by using it.
Keep both versions so you can use older programs that need 2005.