You're missing a major point here! Each process uses 'virtual memory'. That is windows allocates memory to a given process. Each process will use the same virtual addressing. They'll both have a 32-bit range of 0x00400000 - 0x7fffffff for example, but they are 'seperate'! Hope you get what I mean. L. Spiro detailed memory a little in his pointers tutorial, so maybe check that out.
Begs the question though, what are you trying to do? Then we can offer specific advice
~Psych