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As for the getting your iTunes library into your Google Nexus 7, you need to download and install the Google Play Music Manager: Install the Google Play Music Manager - Google Play Help
From there, you will be able to upload your iTunes library into your Google Music account. From there, make sure you have the Google Play Music App installed on your N7. https://play.google.com/store/apps/details?id=com.google.android.music&feature=nav_re sult#?t=W251bGwsMSwxLDMsImNvbS5nb29nbGUuYW5kcm9pZC 5tdXNpYyJd
Once everything is uploaded and synced, you will be able to stream music from you N7.
If you have any more direct questions, please visit our Nexus 7 forums here: http://androidforums.com/nexus-7/