oops, I think the command you were looking for is urpmi.update -a
Anyway, the easiest way to restore the update and other sources is to follow this link:
http://plf.zarb.org/~nanardon/urpmiweb.php
All you need to do is select the sources you want and they will provide the commands needed to add them.
In order to restore the CD's follow these directions:
1. Open Mandrake Control Centre
2. Click on Software Management
3. Click on Software Sources Manager
This will pop up a little window showing all the sources you have configured - which right now is none.
4. Click Add
Here you will get a little window that allows you to add a source
5. Select Removeable Device
6. Give the source a name - "Installation CD 1(x86) (cdrom1)" is what I have
7. fill in the rest of the info
Here is what is listed for CD 1 on my computer
URL: removable://mnt/cdrom/Mandrake/RPMS
Relative path to synthesis/hdlist: ../base/hdlist1.cz
That is taken from the edit dialog box - For the add box, just exchange URL for PATH and fill in the same info.
Hope that works