Maximum ram utilized by CPU?

Actually it's not the cpu that has ram limitations but the OS&motherboard. Windows xp is generally limited to <4gb and often can only utilize 2gb. A cpu doesn't doesn't know the difference between ram and a hard drive. All it knows is that it's processing data from one location or another and that one location(ram) happens to be much faster.

Right, but what I'm saying is that if you have 100GB of RAM, the processor wouldn't be fast enough to ever need that amount of RAM... or am I wrong?

If you are running a 32-bit OS (and you almost certainly are) then you top out at 4GB, if you are using a 64-bit OS (XP 64, Server 2003 64, 64-bit Linux, or Vista 64) then you can address more RAM than you can possibly fit in your motherboard right now.

Additionally, I don't know how it works for other OS's but on XP any non-system RAM memory still counts against the 4GB (i.e. that 512MB GPU cuts your max to 3.5GB etc), and Windows can't assign more than 2GB to any single program unless you tell it to.

You are wrong. The speed of the processor has no real bearing on RAM needs, all that matters for RAM needs is the size of programs. Right now there are almost no programs outside of supercomputers that could use anywhere near 100GB, but is you had a 100GB program then it would still benefit from haveing the entire program in RAM even if the processor was fairly slow.

Cool... that is exactly what I needed to know! I appreciate it!

It's not even the CPU that limits bandwidth across the busses to memory and other parts like the GPU.
It's the socket, for instance a 939 socket has a total bandwidth of about 14gig per second, AM2 about 20 gig per second.
The CPU its self (and I am just guessing here, not researched what the new CPUs actual can process in total bandwidth) is even much higher.

The point is, the amount of RAM you have on your board, no matter how much, will never ever be slowed down by a processor not being able to make use of all of it.

However, the RAM usage is dictated by the program and OS you are running. The processor has nothing to do with it really.

XP pro can support 4GB however...

This is a limitation of a 32-bit architecture. The system can only address 4 GB of allocated memory. Allocated memory is made up of physical RAM, and any I/O space needed by devices. The way memory is allocated is that starting at 4 GB, the system allocated device I/O addresses working its way down. Normally this is not a problem, but when systems have 4 GB of physical memory, the addresses needed to address RAM overlap the space needed for I/O. In this case, the need for I/O space takes precedence, and the amount of RAM visible to the operating system and applications is limited to 4 GB minus I/O space.

For example: If you have a total I/O range of 512 MB needed by all the peripherals, advanced graphics port (AGP) Aperture in the system, you have 3.5 GB shown as usable RAM in Windows.

This changes as you move to a 64-bit operating system.

For example: Windows 64 will be able to address 128GB of memory due to the 64-bit architecture.

32-bit CPU's are limited to a maximum of 4 GB of addressable RAM. 32-bit operating systems may or may not make all of that available to applications. Windows, for instance, only allows up to 2 GB to be used by an application and the other 2GB of addressable memory is only useable by the the OS.

64-bit CPU's have a theoretical memory space of 18,446,744,073,709,551,616 bytes (yeah, that's a LOT). But, there is no architecture today that could power the memory chips needed to hit that limit. Also, while most 64-bit chips can address that amount of memory, they do NOT support enough lines to physically reach that limit. Meaning they can work with numbers that can reach it but they don't actually provide a physical path to that much memory.

64-bit operating systems have the same limitations as 32-bit ones, which is to say they are limited by available physical memory and swap file space. Needless to say, 64-bit computing isn't going to hit its maximum limits any time soon.

EDIT:

I read what you said incorrectly, but you're saying just what I said, 4GB's usable by the OS.

Entirely likely, I didn't actually read the other responses before I posted. Sorry.  

I have a bad habit of doing that sometimes  .