I do not know of any free exam software for this exam, but I can highly recommend Transcender - they even have a package deal where you can get the 70-461 through 70-463 with a discount. I used Transcender for all three exams and that worked out great.

Note: Try to read the books from MS and get as much hands-on experience as you can before trying out the test-exams, this way you get the most bang for your buck with regards to finding out where you are lacking in understanding/experience.

Just my 2 cents.