If you want realistic textures I would advise you to get a digital camera and take pictures of buildings such as the windows and frames, bricks, decorations etc... You're going to need a paint program like Adobe Photoshop to fix up the textures. It will take some skill and practice to know how to fix imperfections and make certain textures seamless.
If you can't get a digital camera but have a good paint program here is a site that has a lot of photos you could start fixing up for game content
http://www.art.net/~jeremy/photo/public_texture/)
Unfortunately, I don't have a link to a tutorial on how to make a texture seamless.