Ignore the above idiot as he doesn't know what he's talking about and those codes he's given are WRONG.

Installing to the hard drive is ESSENTIAL as it reduces Heat, Noise, Laser ware and tear and REDUCES Load times.

Try clearing your caches using THESE codes:

On the Dashboard go to the System Settings menu, Memory, then press Y and press the Cache Clear Button (Using this method will delete ALL game patches off your system as well as the Temporary Files so you'll have to re-download the updates before you can play your games again), (This method was Introduced with the August 11th 2009 update).

OR

On the Dashboard go to the System Settings menu, Memory, then press Y for Device Options then press X-X-LB-RB-X-X (Using this method will delete ALL game patches off your system as well as the Temporary Files so you'll have to re-download the updates before you can play your games again).

OR

Hold The LB, RB and X buttons while the GAME is loading from the Dashboard and hold until you see the 2nd Bethesda Splash screen (Using this method will clear out Fallout 3's temporary files which means loading and saving will take longer until the files are re-cached).

Do you have the 1.5.0.23 patch installed

Also see here for more information on load times: www.cheapassgamer.com/forums/showthread.php?t=202456 (Just press the Spoiler button to reveal the list).