The title of your post does not match the title of the article.
Basically, Windows 7 comes with a "backwards compatibility mode" to support certain types of Windows XP applications that may have problems with Windows 7. The issue is that that compatibility mode requires a certain feature within your CPU that Intel does not support on all of their chips.
That is all it says.
Many of the cheaper Intel CPU's don't offer the VT that's required at the CPU level. I believe all 7000 & 5000 series consumer-grade CPU's do NOT have this functionality.
Remember, this is aimed squarely at businesses, not the home/consumer market.
You can still run a Virtual Machine w/o all this "XP Mode stuff" with either Sun's Virtual box (free) or VMWare Workstation (not free) and still run XP on your computer w/o VT on the CPU. You just can't run the "XP Mode" thing from MS.
Really, I wouldn't want to use XP Mode anyway. Virtual PC is horrendously slow with disk I/O. VMWare or VirtualBox are FAR better solutions IMO....