Email from iTunes about deauthorizing computer...what to do?

Hi, I received this email recently and i have couple of questions please:

1) What does deauthorize do?
2) I have some music that was copied from my old PC when I switched to mac. I used MMJukebox to rip those songs from CDs so it wasn't in iTunes at all. Now, will that change anything? Will I lose it? I left the CDs at my parents house and I now live in a different country so if I lose the songs then it will be a bit complicated to rip them again.
3) Will it put DRM on my songs or will they stay the same? I have Creative ZEN along with my touch and I would prefer not to have 2 copies of my songs on my computer.

4) I have some of my songs in my library twice as I didn't know that when you import a folder that has also .m3u playlist then it will add it there again but when I try search for duplicates it won't find them as the system automatically added name-1.mp3 to it so what is the best way to get rid off them except manual selection? ( I have like 700 of them so to go through them all would take a lot of time.)

Thanks in advance for any help. I appreciate it
Now the email :


Dear Customer,

We have found, and addressed, an issue with your iTunes Store account which was preventing your computers from authorizing certain tracks properly. This problem could affect playing back purchased music or videos or launching applications on iPhone or iPod touch. You won't notice this issue until you attempt to authorize a computer to play one of the affected tracks. We have corrected the issue, however in order to authorize the affected purchases on your computer you will need to redownload new copies of the tracks from the iTunes Store. We have added the affected tracks back into your download queue, and they are available for you to download at any time, free of charge.

Before you redownload, please follow these steps to authorize your account and your computer:

1. Deauthorize your account, by choosing "Deauthorize Computer" from the Store menu in iTunes.
2. Select "Authorize Computer" from the Store Menu in iTunes, and re-authorize your account.

Once you've completed the steps above, you can begin to redownload the affected tracks. To redownload, simply choose "Check for Purchases" from the Store menu in iTunes. Make sure that you enter the Account ID "************" when checking for purchases.

We know that redownloading these tracks will cause you to have duplicate files on your hard drive, so we've created a step-by-step walkthrough that will help you eliminate the affected copies of the files.

The walkthrough for removing these duplicate tracks is available at:

http://support.apple.com/KB/*******

After removing the duplicate tracks, you should also re-sync any iPod or iPhone that have purchases from this account. If your iPod or iPhone is set to Manually Manage Songs and Videos, you'll need to restore the device and then re-add tracks from your Library.

Your purchases should now all play successfully. If you experience any difficulty using your purchases, please let me know.

As our way of apologizing for this situation, and the inconvenience that this has caused, we'd like to offer you a Gift Certificate in the amount of 15 GBP.

Your 15 GBP Gift Certificate code is:
******************

To redeem this Gift Certificate, click the link below to launch iTunes and display the Gift Certificate redemption page: