I suggest reading all of Tim Kalamaros's post Pro se or "do it yourself" wills on his "Teklaw" blog. Here is the first on his list reasons not to write your own Will.
1-- Even if the will is drawn up correctly, do I know how to publish and witness it correctly under the law of the place where it will be signed? Do I know who is a proper witness under the law and who is not?
If you want to use Willmaker or some other computer package to draft a Will, I say fine. I think the price of the software is right for that purpose. Take the draft to a lawyer of your choice and let them review and fix any problems.
Meanwhile, go over to "Teklaw" and check out the article in full.