If you use Firefox, I think there's at least 1, probably several, free form fillers that are Firefox Plugins/Addons.
Just install Firefox, then go to tools - Addons, and click "Get more add-ons"... follow links/prompts, and you can search for keywords as well... I actually think I saw one highly recommended using those very instructions just the other day - didn't try yet, but I'm pretty sure it's there.
Also, if you want to use the Google Toolbar for Internet Explorer and/or Firefox, it has some pretty nice form auto-filler methods.
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"If to err is human, then I must be some kind of human!" -Me