Hi TN, I am from iMesh customer support and will do my best to help you.
The iMesh library songs are located locally on your computer, you can find\change the location by going to: 'Menu > Tools > Preferences > Library & Downloads'.
The Default download folder is usually on 'My Documents\My Music\iMesh' . (in case you are using Windows Vista or Windows 7, the default downloads folder is located at: 'C:\Users\Music\iMesh')
Since the files are saved locally, they are not suppose to be deleted upon re-installing the application.
I hope that helps. If you have any further questions, please reply to this post and I will do my best to assist you.