Rokbal- I'm running on the official release version on my main PC along with my netbook. Microsoft just released it to MSDN & Technet subscribers a couple of days ago.
Holyjebus-Preorders were available a while ago for a discounted price however I'm almost positive that offer has expired. The main difference between 32bit and 64bit is that 32bit OS's are limited to addressing 4gb (2^32) of memory total while 64bit OS's are capable of addressing much larger amounts of memory I believe somewhere around 16 terabytes (2^64).
Windows 7 64bit versions have the following memory caps in place:
- Starter: 8GB
- Home Basic: 8GB
- Home Premium: 16GB
- Professional: 192GB
- Enterprise: 192GB
- Ultimate: 192GB