Konnichiwa Kitty Cupcake!
I unfortunately only know how to type in Japanese on a PC, so if you have a Mac, hopefully someone else will be able to tell you.
Anyways, here are the steps to be able to type in Japanese:
1. Go to the start menu on your computer
2. Open the Control Panel
3. There should be a button labeled clocks, languages, and regions or something similar
4. Click the change/add keyboards link
5. A window should pop up labeled "Region and language"
6. Go into the Keyboards and Languages tab if you are not already there
7. Click the "Change Keyboards..." button
8. Another window should appear labeled "Text Services and Input Languages"
9. On the right, there should be a button that says "Add..."
10. Yet another window will open, this one should be labeled "Add Input Language"
11. Scroll Down the List to the "Japanese (Japan)" Link and press the + button
12. A list should appear underneath with check boxes. Check the "Japanese" and "Microsoft IME" checkboxes.
13. Press "OK"
14. It will close the window, and you should be able to see your primary language in the Installed Services window, followed by Japanese.
15. Click "Apply" and then "OK" at the bottom
16. Now, when you are typing, simply press "Alt+Shift", then "Alt+Caps Lock". This will allow you to type in ひらがな. Be sure to press "Enter" after each word/before pressing "Space" or else the computer will automatically change the Hiragana to Kanji, but the Kanji is not always correct. ;)
17. If you need Katakana, follow the steps to turn on Hiragana, but then press "Alt+Caps Lock" once more.
18. To get back to Hiragana, press "Alt+Shift" 2 times. If you want to go back to your primary language, press "Alt+Shift" only 1 time.
If you are confused/can't get any of the steps to work, I'll try and clarify more.
Also, to spell your name in カタカナ、I would guess that it would be ダリアン (Dariann) or だーりアン (Daariann) depending on how you pronounce it.
Hope this helped!