This site may help you.
Without knowing whether you have a MAC or a PC, Windows or not, this would be difficult to say. The computer and the software would determine the program you would need.
Here is a site about International Keyboards and Fonts:
Here are some other sites to help you:
5. (xp): http://answers.yahoo.com/question/index?qid=20071021100845AAmrn1w
6. (in UK): http://www.ukstudentlife.com/Life/Computer/Oriental.htm
8. (Broken Link Removed)
NOTE: I have no installed Japanese Language Software on my computer because "yomi masen!" Please let me know which system works best for you.
P.S. Additional sites on Japanese Fonts:
4. (by classification): http://www.fonts.com/findfonts/searchresults.htm?st=4&cid=Japanese
5. (Windows XP): http://www.microsoft.com/downloads/details.aspx?FamilyID=f7d758d2-46ff-4c55-92f2-69ae834ac928&DisplayLang=en
6. (Yahoo Japan): http://docs.yahoo.com/docs/info/bridge.html
If you were looking for a QUICK answer = "Ton demonai"