The extension should be r followed by two zeros and not two Os.
When using winrar to extract it, if the second file is detected, you'll see the following:
And if it doesn't detect the second file, you'll see this:
If you try to extract it when it doesn't see the r00 file, you'll get the following window asking you to browse to its location:
From there, you can select the r00 file, even if it's named something completely different and it will continue the extraction using the file you select, assuming it's not corrupted.
If that doesn't solve your problem, you're gonna have to describe in as much details as you can what you're doing because with the information you've given, I'm not too sure what the problem is other than maybe the files aren't named properly or haven't been downloaded properly.
