Like what was stated before, the difference between hiragana and katakana is katakana is used for words foreign to the Japanese language.

I'm learning Japanese in college, and I can tell you that the kanji is, at times, unneccessarily difficult. But the thing to remember is that it has evolved over time from paintings/pictures to the symbols we know today, so trying to 'see the picture' each one represents helps sometimes. One thing that helps me is http://www.nuthatch.com/java/kanjicards/ which my teacher sent me to help with memorisation. Or, if you want a more tangible source, there's a book called 'A Guide to Remembering Japanese Characters' by Kenneth G. Henshall, which details the history of different characters, their applications, and the number of strokes needed to write them.

One other way is to get Japanese penpals who are willing to teach you, like you can find at www.japan-guide.com . There are a lot of people willing to teach you Japanese in exchange for English lessons, and you get a friend out of the deal as well.