go to project-new project- save with any name->atmel->select AT89S52 or any IC you are using->start up code->no->new icon(down the file icom)->save as name.asm->copy your prgm in it n save
right side-> source code-> right click ->add files to group source->select asm->add->close ->
right side->click on sourse code ->select your prgm go to build target->it wil automaticaly creat hex code at the place where your asm file is been saved.
Or else you can use online assebler by using following link
http://www.8051projects.info/onlineasm.asp