Searching process memory for value

[astro]

Hello,
I am trying to make a small utilty that will search a process's memory for a specified value. I am currently able to both read and write memory values. But I'm not sure how I would go about scaning the memory for a value and getting it's base address.
The program can read arbitrary memory locations with specified lengths. But how do I know where (What memory location) to start searching from and where to stop searching. I believe it has something to do with using the mapped memory files but not sure.
Could someone please enlighten me on how to do this or point me towards a resource which will help me figure this out?

Thanks!

[PanGalactic]

Will the utility be used to search its own process space, or is the goal to search another process's address space?

[astro]

It will be used to access another process's address space

[PanGalactic]

You probably want to have a look at how a debugger such as gdb gets access to another process space. You will have to use similar hooks I think.