You most likely get the error because you haven't selected anything on the listbox yet. You need to bind the listbox to the mouseclick that does the selection and to a function that contains your get(index) code. Something like this:
[php]from Tkinter import *

musicfolder = [
["CollegeRock/"],
['RnB/'],
['HipHop/'],
['Build/'],
['Buy/'],
['Techno/'],
['Jazz/'],
['Classic/']
]

def get_list(event):
"""
function to read the listbox selection
and put the result in an entry widget
"""
# get selected line index
index = listbox1.curselection()[0]
# get the line's text
seltext = listbox1.get(index)
# delete previous text in enter1
enter1.delete(0, 50)
# now display the selected text
enter1.insert(0, seltext)

root = Tk()

# create the listbox (note that size is in characters)
listbox1 = Listbox(root, width=50, height=6)
listbox1.grid(row=0, column=0)

# create a vertical scrollbar to the right of the listbox
yscroll = Scrollbar(command=listbox1.yview, orient=VERTICAL)
yscroll.grid(row=0, column=1, sticky=N+S)
listbox1.configure(yscrollcommand=yscroll.set)

# create data entry
enter1 = Entry(root, width=50, bg='yellow')
enter1.insert(0, 'Click on an item in the listbox')
enter1.grid(row=1, column=0)

# load the listbox with data
for item in musicfolder:
listbox1.insert(END, item)

# left mouse click on a list item to display selection
listbox1.bind('<ButtonRelease-1>', get_list)

root.mainloop()
[/php]

thank you for the code. sorry for the delay.