Automatically fill out form MySQL db

I want to log in to a page and then automatically submit a form. The form's data is drawn from a MySQL db. I know PHP Curl a bit but I believe it can't handle javascript or ajax-based forms well. I briefly read about Java's HTMLUnit and it seems like this can handle ajax created forms too but I'm not certain. If there are multiple pages then it would be nice to automate this but for now I don't mind if I have to click on the next button to get to the 2nd page of a form and then automatically fill out this form's data from the MySQL db. I don't mind about the captcha either. Right now I'm using Roboform to automate some of that tasks but the data is not drawn from a MySQL db and I have to copy and paste some of the data from an excel sheet. I'm open to suggestions on whether to use PHP Curl, Java or some other way such as Roboform or even a plugin for firefox. I would like it to be flexible for use on Vista/Windows 7 AND Mac OSX platforms. Please let me know the cost and time frame.