http://www.any-video-converter.com/products/for_video_free/
There's a nag at the end of the conversion, but you can set the frame size (in case there's a limitation of e.g. 720x576 with your player) and the video and audio bitrates (according to the quality required).
Bear in mind your H.264 files are your originals, and an XviD AVI conversion could be a 1/3rd larger filesize for the same quality, but will also lose something due to being compressed a second time.
Media players that will play H.264 are available. You can hook up an external hard drive or plug in a USB card reader.