Hi,
Basically integration testing can done in two ways 
Top-down approach and Bottom up approach.
in top down approach we can use stubs.
in bottom up approach we can use drivers for integrating 
the modules.using drivers for each new module being tested 
in integration with all lower-level modules.
eg: we need to integrate 3 A,B,C modules then by using this 
approach the lowest-level modules "B" and "C" are tested 
with drivers. Next, the higher-level module "A" is tested 
with a driver in integration with modules "B" and "C." 
Finally, integration could continue until the top-level 
module of the program is tested (with real input data) in 
integration with the entire program.

In Bottom Up approach, the Child modules are developed 
first. As the parent modules are developed, they are 
integrated with the Child modules to perform integration 
testing. In the process, if at all any parent module is 
missing, inorder to continue the integration process, a 
temporary program (called as DRIVER) is submitted in the 
place of parent module.

drivers are simple program designed specifically for 
testing that make calls to these lower layers......