These attacks attack the kernel. Which is the core of the system. They are based on flash and other items that you just view. From there someone can take over your PC.
That is why even the US Homeland Security has advised everyone to update to the latest patch. There was a major flaw in XP that could allow someone to take over your PC jsut by viewing a flash item. I dont think you wish to take flash off from websites.
At issue is Microsoft patch 06-040, which involves a flaw in the Server Service function of Windows. Affecting all versions of the operating system after Windows 2000, a buffer overrun could open up a remote code execution risk that could result in a system takeover.
Various security firms also echoed the DHS' concerns. eEye Digital Security said that exploit code had been found in the wild, and that the vulnerability was being exploited in the wild as a "zero-day" attack. Unpatched systems run the risk of being infected by a worm attack, which is considered imminent, the companies added.
So as you see using Longhorn would not allow for you to have this patched and therefor very open to attack. This is only 1 of many major problems. The Window Picture and Fax Viewer isnt patched which was taken advantage of in December. That is just the begining of the list. I cant even remember all the patches that have come into effect sinec the old Longhorn builds.
This is why i advise against it at all costs. Even if you use a Anti-Virus and Anti-Spyware you will still be open to attack.