IMHO there's really no need to take a simulation... the best thing that you can do to pass this exam is make sure all your basic skills are brushed-up on... the questions in the test are VERY straight-forward multiple choices... to brush-up before the linux+ test i went through this very basic IBM tutorial and it was actually quite useful:
http://www-106.ibm.com/developerwork...-lpir21-i.html
anyways, if you simply wanna get an idea of the wording and stuff of the questions i googled this site:
http://www.cert21.com/CompTIA-exam.html
seems like they offer a free demo which you can check-out...
i've never tried those demos so i can't vouch for them, though...