Does anyone know where I can find a book of the Old Testament? My sister wants to read it. Thanks in advance fofr any help.

It would probably be easiest to buy a whole Bible, rather than look for a book containing only the Old Testament.  The Old Testament is contained in the first portion of the Bible.

Christine:  Your sister can find a digital version of the Book of Isaiah in its ancient form, on-line.  Google (working with the Israel Antiquities Authority) has begun posting digital versions of the Dead Sea Scrolls, discovered in 1947, on-line for everyone to view.  The images of the scrolls are in their original format and language.  The site also provides translation tools.  It's dss.collections.imj.org.il    If your sister wants to get acquainted with the other prophets (major or minor) she can find copies of the Bible cheap at any thrift store such as Good Will, or can even ask the Gideon Society for one.  I suppose she could maybe just keep one of those Gideon Bibles one finds in hotel and motel rooms everywhere.

There are various websites that have the bible in the multiple versions.  It would be well worth it for her to do a comparison of the different versions to see which one clicks with her.

When I read for understanding, I read the NIV (New International Version)

When I read for beauty or memorization I use the KJV (King James Version)

For the longest time I used a parallel Bible with King James on side and The Living Bible on the other (The Living Bible is funny in spots due to the translation sometimes using VERY modern colloquialisms.

Here is a site which has a TON of versions to compare to find out what might be the best fit for her:

http://www.biblestudytools.com/philippians/4-13-compare.html

This might be right what she needs.  It looks like you can get her a Bible for free.

http://www.biblesenders.org/

In her request, make sure that she specifies that she wants to Old Testament AND New Testament.. becauase some BIble are new testament only.

I agree with the others, buying a whole Bible would be easiest.  The translation you choose would depend on what you want to get out of the reading.  If it is a first time reading for general understanding you could choose a reader friendly "the message" or if it is academic I would choose a more strict translation.

It looks like one is available here on this site: 

http://www.paperbackswap.com/Holy-Bible-New-International-Bible-Society/book/406805/