VooD and I have come up with an .xbe patching utility that allows you to change the settings of the Flicker Filter used in-game.

What is FlickerFucker?
FlickerFucker (FF) is a windows based, xbox executable patching utility which changes the behaviour of the default FlickerFilter settings.
The FlickerFilter is a bit of hardware built into the xbox itself, which can be controlled by software. Due to a television's slight over and underscan when drawing a screen, there is often a bit of jumpiness and flicker on finely drawn details, such as text. To keep text from being too jumpy, the FlickerFilter allows the image to be blurred slightly, which reduces the amount of jumpiness in trade for image sharpness.
Virtually every single xbox title defaults the FlickerFilter to a value of 5, the maximum amount of blurring available, and offers no means to reduce the amount through in game options.

FF allows you to force the amount of FlickerFilter used in a game. You can turn it off altogether or select any amount of flicker filtering between 1 (minimum) and 5 (maximum).
Obviously this is only true for Standard Definition Interlaced TV´s (15khz), and the benefit will be proportional to the quality of the cables used for connecting the Xbox to the TV (best results with Scart RGB cables, worst with composite cables)

This utility is a generic .xbe patcher, so we've also put together a compatibility list that anyone can edit with their results. Some games are finicky and can't be changed, but I think we're getting about a 90% success rate in being able to change the default values that the game uses. Give it a shot, the effect is somewhat subtle, but interesting to play around with, and may give some of your old blurry games a new life to your eyes.

Official-Site: http://xbox.nugnugnug.com/FlickerFucker/