That's a good question. I can see why there might be some confusion. 
 
Our canon of scripture is made up of four books: Bible, Book of Mormon, Doctrine & Covenants, and the Pearl of Great Price. We use the King James Version of the Bible. They are all considered scripture and equal with each other. 
 
We absolutely love the Bible. I can't imagine not having all the stories and historical record of our Lord and Savior, Jesus Christ. The historical record in the Old Testament points us to Jesus Christ and helps us understand His importance and the importance of keeping His commandments. The epistles and other books of the New Testament help fill out our understanding of Jesus and the Church He organized. The LDS Church could not be complete without the Bible. We have to have it. 
 
In our church services - we have what we call Sunday School. It usually lasts about one hour every Sunday. We have a rotating course of study for Sunday School. This rotation is on a four year cycle. A full year is dedicated to each topic area. The four years of study are: 
- New Testament 
- Old Testament 
- Book of Mormon 
- Doctrine & Covenants/Pearl Of Great Price/Church History 
 
We do the same thing with our teenagers. During their 4 years of high school - they take a class called Seminary. In most of Utah, Idaho, and some other places it is a regular class as a part of their school curriculum. (Seminary is held at a separate building off-campus from the high school.) For the rest of the part of the world - there is what is called Early Morning Seminary. In the city we live it goes from 6:10am - 7:00am every school day. It is held in our church building. They follow the same four years of study. So you can see from that - fully 2 of the 4 years of gospel study is dedicated to the Bible. That is twice as much as the Book of Mormon. 
 
At the same time - there might be a perceived inequality between the Bible and the Book of Mormon. According to our 8th Article of Faith: "We believe the Bible to be the word of God as far as it is translated correctly. We also believe the Book of Mormon to be the word of God." The Bible and Book of Mormon fit together like two gloves. They are both needed. This is not to say that the Bible is not true. It absolutely is. It's just that through multiple translations and multiple hand-written copies (i.e. monks) through hundreds and thousands of years - there has entered into the current Bible translation some oversights or mistakes. Some of these were inadvertent. Some were intentional. All that means is that when reading the Bible we accept what is says, but that there might be some things we need to study harder to understand the meaning of the original author. I dare say that we accept and believe the Bible more than almost all other Christian religions. In fact, with the additional light and knowledge we have received through modern prophets and modern scriptures - I would claim that we believe and live the concepts and teachings of the Bible more than any other religious group. 
 
So why is there the perception - even among some mormons - that the Book of Mormon has pre-eminence over the Bible? Because the Book of Mormon has gone through a literal translation through the gift and power of God - we believe that the Book of Mormon has been able to capture and convey the pure spirit and meaning of what was written more powerfully and spiritually than the Bible. The Bible is absolutely true. However as it has gone through the changes and translations through the centuries it does not have the pure language and spirit as when it was originally written. 
 
So we absolutely believe the Bible is true, but more importantly we believe and live the teachings in the Bible as they were intended when initially written. So it's not that the Bible is false or less authoritative than the Book of Mormon - it's just that the we at times need to read the Bible through the glasses of modern revelation to understand it's true and pure meaning. With the Book of Mormon we believe that when Joseph Smith translated it under the gift and power of God - it was able to keep the true spirit and meaning of the translation. That's why we believe that the Book of Mormon is the word of God without any qualifications. 
 
Let me finally say - there is a special spirit and power with the Book of Mormon. (Not to say that there isn't with the Bible.). When one reads the Book of Mormon a special blessing and spirit from God will abide with the reader. It is very powerful and has led to the conversion and retention of millions and millions of readers. If you take the time to sincerely read it - you can also feel the power and spirit that accompanies it.