As Matt rightly says, your experience won't count in the aptitude tests, because ultimately they are there to find out if you have a natural aptitude for the job. Once you get to an interview then you are likely to do well considering the interest and experience you have, although it's not guaranteed.
Give it a go - you have nothing to lose and everything to gain. Get past the first hurdle (the tests) and get on to the second hurdle (the interview) where it really will be up to you.
And Good Luck!
Cheers,
N
"Keep smiling, it makes people wonder what you're up to..."