This site has instructions for setting up the mirror sources for everything. You just follow the instructions, then at the end, you open a terminal/Konsole window, su to root and then copy and paste the output of the last box into the terminal. Sometimes you have to hit enter, sometimes it'll kick off automatically.
Theres a few other options if you look round the software manager in the mandrake control centre (configure my computer), if my memory serves me correctly, the software manager has the options for deleting sources - which I always used to do before getting the output from Easy Urpmi - that way, I only got the option to update from the new sources, and not anything pre-configured by mandrake and/or the discs.
PLF source mirrors where good ones to use, as they often had more up to date packages available, and had also often been customised with some eye candy stuff.
maybe that helps some ???
regards
John
p.s. Oh and often if I got replys like the one you quoted, I'd just drop/delete the sources mirror stuff and then go to easy urpmi and get different. You'll often find that replies like that are caused by the mirror you're using being busy. If you can wait, then try again later. Or just try different ones e.g. the UK listings mirrors often were busy, so I'd try the ones in Holland, Denmark or Scandanavian ones. In your case, you could try any of the ones within North America - If I remember correctly, theres quite a few.