"The XL2420T is also a great choice for extreme entertainment. It is certified as NVIDIA® 3D Vision™ 2 ready, providing gamers with full HD 3D gaming and entertainment experiences like never before. For more vivid viewing, it also comes with the NVIDIA 3D LightBoost™ technology for up to twice the original screen brightness. The XL2420TX is embedded with a 3D IR emitter and comes with an NVIDIA® 3D Vision™ 2 Glasses Kit for a truly immersive 3D experience with no hassles."
People were also stating there is a difference with the T version if you do try and use 3D with it. It had something to do with the monitor not supporting a certain Nvidia format. I don't know a lot about 3D, but people that purchased the T monitor were very angry because it doesn't work with the glasses they already had...
I guess in the monitors manual it clearly states this but the website doesn't have any information on it. You may have to do some google searches... sorry to be vague.
Anyway if you aren't planning to use 3D get the T not TX.