How To Use Acronis Backup on a Brand New Replacement Hard Drive

I'm sure my problem is covered somewhere already, but I sure can't find it.... Simply stated, how do I use my existing complete backup done on Acronis True Image 2011 after a complete hard drive failure? My Asus computer is being repaired at the manufacturer and they are replacing the failed hard drive with a new one which will have Win7 on it and whatever other Asus software on it that the original had originally, but nothing else. Fortunately, I was completely up to date on my backups, but do I have to try to install Acronis True Image 2011 on the new drive in order to make my backup work? Do I have to rebuy it? Can I buy a newer version and have it read my backups on Acronis 2011? Don't ask me what type of backup I have done, because I don't know.... all that info is on my external hard drive used for the backup, but how can I read it if I don't have the software installed anymore? As you can tell, I'm a complete novice anD have always hoped I would never have to use this software for recovery from a complete disaster.