iFlashCards looks for folders in the /var/root/Library/iFlashCards directory on your iPhone. Create a folder with a questions.txt and answers.txt file with the question and answers listed one-per-line and place that folder in the /var/root/Library/iFlashCards directory. When you launch iFlashCards select the desired folder and start learning!
A sample flash card directory is in the downloads page (GRE-Vocab.zip). Simply extract and copy the folder as explained above to learn your vocab! http://code.google.com/p/istudy/