[Bri]

MS has a trial of XP Pro 64, which is the migration to Vista 64.. best to setup as a dual boot in case you have "antique" apps or devices. However, once you get hooked on the speed... then

If you purchase a computer with a 64 bit processor (not an Itanium), you can obtain an OEM System Builder Copy of XP Pro x64 from many vendors, with a qualifying hardware purchase. This hardware must be a non peripheral item that becomes an integral part of the system . Ordering additional/replacement RAM for your system and installing it fulfills the requirement.
Additionally, the original license for the 32 bit version of Windows XP Pro is still valid if you obtain a copy of x64 in this manner, enabling you to keep a dual boot as long as you want or need to...

PS: Tis a short learning curve for the developer writing code for 64-bit Windows.. is just like writing code for 32-bit Windows.
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RL..now with 100% less lag!