One Mb is (1024*1024) bytes, so 733000000/1024/1024 is under 700...
You should always check the MD5 checksum after downloading anyway (k3b does it by default). You don't have to start a new CD layout / project / whatever your burning SW calls it, but simply burn the downloaded cd ISO image as is (menu File/Burn Image with Nero). Once your cd boots you can also start "knoppix testcd" to have some self-test run.