RAM limit is 128 GB, I believe.
A key difference between 32-bit and 64-bit computing with Windows XP is that the 64-bit version can use more system memory. According to Microsoft, Windows XP Professional x64 Edition supports up to 128 gigabytes (GB) of RAM and 16 terabytes of virtual memory.
That enough for what you are planning? :)
For more info, pl see the Microsoft XP website [http://www.microsoft.com/windowsxp/64bit/facts/top10.mspx]
Hope this helps.
JianMei