As you know, the music tracks purchased from iTunes store are protected by DRM. You can only play them on Apple iPod, iPad and iPhone and are limited to play on five Apple devices only. So if you want to play iTunes music with your Galaxy Tab, you need to remove iTunes DRM and convert iTunes music to (DRM free) audio files first.
The easiest way is to burn the music to an audio CD in iTunes and then rip it back as mp3 files.
Or you just get TuneClone to help you, which works great for converting a great number of music tracks, needs no CD discs and preserves the ID3 tags well. Here is the full step-by-step guide: http://itunesm4ptomp3.wordpress.com/2008/07/04/how-to-convert-itunes-m4p-to-mp3-with-tuneclone/
After you get the output music files, you can then transfer them to your Galaxy Tab.
1. From the Home screen, tap Menu.
2. Tap Settings.
3. Tap Wireless & networks.
4. Select the Mass storage option.
5. Connect the Galaxy Tab to the computer with the included USB cable.
6. Slide down the notification panel at the top of the screen.
7. Tap USB connected.
8. Tap Mount.
9. On the computer, open the drive that represents your device. It should be in My Computer/Computer for Windows users or the Finder for Mac users.
10. Make a folder named Music (not required but recommended for organizational purposes.)
11. Copy the music files over to the Music folder.
12. After copying music, swipe the Notification panel down, tap USB storage, then tap Unmount.
Audio formats supported by Samsung Galaxy Tab include MP3, AAC, AAC+, e-AAC+, WMA, AMR, MIDI, WAV, IMY.
Video formats supported by Samsung Galaxy Tab include H.263, H.264, 3GP, MPEG4, WMV, DivX, Xvid.