It doesn’t matter if you have a motherboard that supports 8GB or 64GB if your OS is only 32-bit. To figure out how much memory a 32-bit OS could see, it would be 2^32 = 4294967296, which is ~4GB. Similarly with 64-bit, 2^64 = 18446744073709551616, much much more. Best bet would be to upgrade your OS to 64-bit Linux or 64-bit Vista.