32 Bit operating systems are able to see (if moded and with a compatible chipset) but unable to allocate more then 2GB of RAM.
"This behavior is due to "memory mapped IO reservations". Those reservations overlay the physical address space and mask out those physical addresses so that they cannot be used for working memory. This is independent of the OS running on the machine.
Significant chunks of address space below 4GB (the highest address accessible via 32-bit) get reserved for use by system hardware:
• BIOS – including ACPI and legacy video support
• PCI bus including bridges etc.
• PCI Express support will reserve at least 256MB, up to 768MB depending on graphics card installed memory "
If u want 4GB or 3GB of ram u should get any modern motherboard/processor and pair it with a 64 Bit Windows.
3GB in triple channel mode on the X58 is faster due less syncronization needed, less memory sticks are always faster if the amount of memory is enought to cover your work - not to mention that triple channel > dual channel (even if not much) and ddr3 > ddr2 (again, even if not much).
If u want triple channel you need three identical sized modules, some chipsets will work with different size modules but the extra memory on the bigger module will not be used. Using 3GB on triple channel plus 1 GB on single channel is possible if the chipset allow it on multiple CPU boards - maybe unggaged mode -, single CPU boards cant do it.