You can run the application file of project in simulator - not .ipa file.
You can get it from:
Libraries-->Applicationsupport-->iphone simulator-->4.3(its ur simulator version)-->applications-->
then u can see many files like 0CD04F....
find out your application file through open it.
You can copy the file to your system(which system simulator u need run ) location Libraries-->Applicationsupport-->iphone simulator-->4.3(its your simulator version)-->applications-->
Then open the simulator 4.3 (its your simulator version where you pasted). You can see the application installed there.
Getting from other people:
Please tell them to find out Libraries-->Applicationsupport-->iphone simulator-->4.3(its ur simulator version)-->applications-->
then you can see many files like 0CD04F....
from their system and receive that file from them.
After they have got the file, please copy and paste the file in to your system `Libraries-->Applicationsupport-->iphone simulator-->4.3(its your simulator version)-->applications-->(paste the file here).
Then you can see the app is installed in your system simulator and you can run it after clicking the file.