The CPU E5200 supports both OS 32 bit and 64 bit.
You wont see the difference whether it is optimised in 32/64 bit. If you are using a lot of memory, it is good to try the Windows XP 64 bit to see how much it allocates as reserve amount.
So i will say that this is entirely up to you which Operating System you want to use whether it is 32 bit or 64 bit.
Memory Limits in Windows
Limits on memory and address space vary by platform and operating system. Typically, 32-bit versions of Windows XP and Windows Vista are limited to 4GB. To take advantage of system memory greater than 4GB, all the following components must support 64-bit:
Refer to Enabling 64-bit Desktop Computing
In addition, the 32-bit versions of Windows will reserve a portion of memory for critical system functions such as chipset, BIOS flash, PCI Express, etc. If you have 4GB installed, Windows will indicate less than 4GB is available (example: 3.24GB). Your desktop board’s Technical Product Specification includes a detailed system memory address map.
I know for sure that if you are using 8gb memory, desktop without onboard graphics and windows xp 64 bits, the memory will be 7.93 GB in Windows, which is pretty good.
Now if you would like to have some more information on Windows 32 bit and 64 bit, may be you can check on this website:
Hope these information will be of some help to you.
Since you have just 4GB memory, i cannot see much if it would really make a difference for you.
May be you can read a bit on this website as well: