It's T- minus three weeks until the launch of Windows 7 (ending the long national nightmare known as Windows Vista). However it's been a matter of concern, especially for smaller businesses, what would be the pain factor for those organizations not ready to give up their programs meant to run on XP.

Microsoft is promising to make it painless. Windows 7 will ship on October 22nd, with a special "XP mode" available that runs on Microsoft's Virtual PC technology.

Here's the laundry list of what you need to know:

1. The PC needs at least 2GB of memory.

2. It also needs "chip level virtualization". This is tricky. Most people don't really know if they have this. In true Microsoft fashion; they assume those that need it, know they have it.

3. XP Mode doesn't actually come pre-loaded into Windows 7. You have to download it from the Microsoft site.

4. XP Mode is only available for free for the Enterprise, Professional or Windows 7 Ultimate versions.

5. Good news: Users can go seamlessly back and forth between the two operating systems. Your XP appications will have short cuts on your Windows 7 toolbar.

6. Bad news: two operating sytems means security software loaded on each. XP Mode is not protected by whatever security applications you are running off Windows 7.

Footnote: my colleague, Beswick Channer, has actually been running a preview copy of Windows 7 since April. He says it hasn't crashed once and his machine only has 512MB of RAM. I'm impressed!