If the linker errors are bothering you that much then jut add the source for SDL_image into your project, you are going to need to link to a few other libs if you do though - zlib, libpng and jpeblib but if you are only using PNG images you could just rip the PNG loading code.
Then there's something seriously wrong with either your linker or your setup.
You can get a copy of VS.NET academic for around $100 or so, or you might even be able to find a copy on eBay or something similiar. It's definitely worth the investment but your situation may not allow it.
You probably have sdl_image downloaded from http://devpaks.org/. right ? that pack was fscked last time i checked. download its source code and build the lib yourself or PM me for my libSDL_image.a and SDL_image.dll files.