"So my question is do they support operating systems like
Windows 2000 Prof., Windows XP or i have to go for their 64 bit versions?"

In this sentence "they" is equal to the CPU's Celeron D, Pentium D or Pentium 4 Processor. The answer is simple. Windows 2000 and XP all run fine on these CPUs with or without the Execute Disable Bit.

Hope this helps.