MadBoxPC posted a comparison review between Geforce 8400GS and
Radeon HD2400XT in Spanish.

Are you ready for a High Definition HTPC? We tried a Geforce 8400GS and a Radeon HD2400XT, both with 256Mb video memory and H.264 video decoder and Multi GPU capability. As usual, we also did some overclock tests on them.

Read more (Spanish)
Read more (with translator)