lets start off first by understanding what a grid computer really is...imagine you are using your dad's old Pentium 2 machine which is working like one hell of a supercomputer...OK! OK! its a stupid example but one day this would be a reality, this is where the grid comes in :)...although work and research are still being done on it but it is possible to make a computer do the job on request of another... and in some case if that computer isn't able to another would take care of the job...in short the computers are sharing their resources(Hard Disk, Memory and Processing Power)