Yes its fine to install..
Instructions:
1. Download the new Android market applications .apk file.
DOWNLOAD LINK:
http://www.multiupload.com/2TRUW4L630
2. Enable non-market apk installation. Go to Settings... Applications... turn on the “Unknown Sources” checkbox at the very top. Accept the warning which pops up by tapping on OK.
3. If you downloaded the file on your computer, transfer it to your phone.
4. Open your file explorer app (if you don’t have one, download any file manager from the android market) and browse to the location where you transferred the file to.
5. Tap on the file to install it.
This will replace your existing market app with the latest market app which adds the new movies and books feature.