Click the iTunes menu, pick "Preferences", click "General" (should be the pane that comes up first), look down toward the bottom right side, for "Import Settings". Click that, and in the next window, click the drop menu "Import Using", pick Apple Lossless Encoder, and "Setting" should be set to "Automatic". That's it, you're set. Everything you import will come in bit-perfect, Apple Lossless.
If by "Streamer" you mean an on-line purchase source, iTunes will play everything natively except FLAC and OGG. If you want, there are ways to get iTunes to play FLAC but it's sort of a pain, or there are converters that will create bit-perfect AIF or Apple Lossless copies of your purchased FLAC files. It's a bit of a google project for you...but there out there. I found this:http://www.bigasoft.com/articles/how-to-convert-flac-to-apple-lossless-audio.html