I wouldn’t even worry about this, if you have 4GB of RAM the 32 bit OS will use as much as it can handle.
Here is an extract from an article in the Windows Secrets newsletter by Scott Dunn who is vastly more experienced than I in this matter.
Here's the full story behind how much RAM a given system can handle.
First, there’s hardware. Each system has a fundamental physical limit on the amount of memory it can accommodate. Most PCs and laptops sold today have a 32-bit internal architecture.
That means that the computer can generate distinct, internal memory addresses that start at zero and go up to a binary number (ones and zeros) that’s 32 digits long. Mathematically, that’s 2 to the 32nd power — or about 4.2 billion memory addresses to play with. This translates to about 4GB.
The 32-bit limit is fundamental and real: a 32-bit PC cannot generate an internal 33-bit address, so once all 4.2 billion addresses are in use, you’re done. About 4GB is all you get for RAM in a 32-bit PC, period.
Why “about” 4GB? Why isn’t it an exact number? That’s because the PC uses its total memory space not just for RAM but also for such housekeeping chores as remembering your hardware and maintaining internal scratchpads and “stacks.”
Any memory addresses remaining unused after the housekeeping requirements are met will be available for use as general-purpose memory. This represents the amount of RAM you can actually use.
It’s not unusual for a PC to need almost a full gigabyte of addresses for internal use, so putting 4GB of RAM into a standard 32-bit system usually nets around 3.2GB of usable RAM. The rest of the 4GB of RAM is there, but the system has no way of accessing the memory because your PC has run out of internal addresses.
There’s a further complication: many current systems — especially laptops — don’t even try to allow the absolute theoretical maximum RAM due to such design considerations as cost, heat, power consumption, and size.
That’s the hardware side of things, but standard 32-bit software also shares the same mathematical ceiling that 32-bit hardware has and is likewise limited to recognizing no more than 4GB of address space.
That’s all the RAM that standard 32-bit XP or Vista (or 32-bit Linux or Macs, for that matter) will ever “see” on standard 32-bit hardware. No matter how you slice it, 2 to the 32nd equals 4GB. That’s all there is.
Note that some server-oriented 32-bit systems can use “address extensions” to perform a sleight-of-hand that tricks the operating system into thinking it’s working within the normal 4GB address space when the system is actually tap-dancing madly behind the scenes to allow access to somewhat more.
Scott Dunn covered some of these techniques in his excellent column in the Dec. 18, 2008, newsletter titled “Access more memory, even on a 32-bit system.” But even though the techniques Scott describes let you partially sidestep current memory constraints, they don’t change the fundamental 4GB cap for 32-bit architectures.
The real answer for more memory space is to move to 64-bit hardware and software. The mathematical ceiling for 64-bit hardware is an astonishing 16EB (exabytes) of memory space — 16 quintillion bytes. That’s a whopping 16 million terabytes, or 16 billion gigabytes. That ought to accommodate your MP3 collection.