dilemma in deciding which OS (64bit or 32bit) to install

hai
i bought a PC with Intel 946 original motherboard with P-IV Dual Core 2.8 GHz processor
i’m running winXP Pro and now when i try to
install Redhat Enterprise Linux i’m unable to
progress with both the types (64bit and 32 bit versions)
first of all i dont know my processor’s architecture. how do i come to know that?

krish….