How do I upload Cyanagenmod when the only things I have access to are Download mode and ClockworkMod recovery?
In recovery mode, use this:

adb shell mount /sdcard
adb push {filename} /sdcard/{filename}


UPDATE #1: An alternative suggested by ce4: 


  Pull out the SD card, copy all needed files externally, and put it
  back in


UPDATE #2: It seems the user did not install CWM correctly. After fixing this, adb push now works as expected.