If you install Recover My Files on the CD there is a small risk that you could overwrite and destroy deleted data. Recover My Files is 6mb in size so when installed it will take up 6mb of disk space.You would have to be very unlucky, but there is a small risk that this disk space could contain the data that you want to recover.
There is also a risk that if you continue to use the computer Windows will write data to the disk (it does this as part of its normal operation) and you could be unlucky and have it overwrite your important files.
The best option is to remove the drive and connect it to another PC as the secondary drive as this greatly reduces the possibility that Windows will do this and then you can install Recover My Files on the other drive.
If you cannot do this, the best option is to use another computer to create a Recover My Files CD and run it directly from the CD. There are futher instructions here:
http://www.recovermyfiles.com/data-recovery-cd.php
I hope this helps.