Heh, I wonder if ubuntu comes with nano or pico. For such a simple task vi would be enough 

To copy it:
cp sources.list sources.list.bak
To edit it:
vi sources.list :twisted:
(of course, without the smiley)
Quick vi:
You move with the arrows.
If you want to edit, press 
i or 
Insert (should appear INSERT in the last line).
To quit "edition" mode, press 
ESC.
-- Next commands must be entered out of the "edition" mode, and press ENTER after each one --
To save type 
:wTo save and quit type 
:wqTo quit if you haven't made any changes type 
:qTo quit if you don't want to save the changes type 
:q!-- More --
To go to line # type 
:# (replace # by the line number you want to go).
To find string str type 
/str (replace str by the string you want to search). Direction = Down.
To find string str type 
?str (replace str by the string you want to search). Direction = Up.
To repeat last search type 
//. Direction = Down.
To repeat last search type 
??. Direction = Up.
To repeat last search press 
n (this one doesn't need ENTER). Direction = Same.
To repeat last search press 
N (shift + n) (this one doesn't need ENTER). Direction = Contrary.
To undo press 
u (this one doesn't need ENTER).
[edit]
Dunno if it got installed or already came with Kubuntu Dapper, but I have pico and nano. You can try those first which are a lot more friendly 

[/edit]