Why are there no cheat codes for "NBA Live 2005" or "NCAA March
Madness 2005" on the Xbox console system? Both games even have a
"cheats screen" (in the lounge) where you can enter cheat codes, yet
I'm still unable to find codes ANYWHERE!

For cheats to NBA Live:
http://www.usatoday.com/tech/columnist/marcsaltzman/2004-11-23-saltzman_x.htm

For NCAA March Madness:
http://www.cheatcc.com/psx2/ncaafb2005.html
(this one is meant for playstation but might work with xbox)
or try:
http://www.cheatcodesclub.com/search.php?gamename=NCAA%20Football%202005&system=all

:)

NBA Live 2005:
http://www.gamefaqs.com/console/xbox/code/920478.html

NCAA March Madness 2005:
http://www.gamewinners.com/playstation2/NCAAMarchMadness2005.htm

There isn't out there much for March Madness, but I'd keep checking
both of those sites for more codes as the games are aout longer. 
Gamefaqs will eventually have the March Madness cheats available as
well.

Thank both of you very much!

There are a ton of them at Xbox Cheats .com:
http://www.xboxcheats.com/cheats/NBA-LIVE-2005.shtml

By the way, Xbox Cheats is the official supplier of Xbox cheats to
Microsoft's Xbox site and is featured by Microsoft here:
http://www.xbox.com/en-US/xboxcheats/default.htm