merlin, actually searching is not a problem.
Like VOX said, you must use ReadProcessMemory
If you see the description of the function, you'll find that it starts searching from a *BASE*address, now you do your string search using any alog( boyer moore is you like ) and you find the location.
Add it to the base and you get the virtual address in the running process.

If you still have a problem maybe you could be a bit more specific?