Altera university program offers an sd card IP controller in spi mode. Is that good for you? If you want a faster communication protocol - like 4 wire - then you need to create your own sd card controller or buy a license for a premade core (the SD card communication protocol is really complicated). Additionally, to read txt files you need to have a FAT file system interpreter in your C code.
I've been working on an open source 4 wire sd card controller (
http://www.alteraforum.com/forum/showthread.php?t=48229), its not complete yet. You can find open source FAT file system code as well and use it as part of your stack.