Well, I have been using VirtualBox for ages in PCLinux and find it works just great to run Windows XP and the apps in it I need, namely Word Publisher which there is no compatible alternative to in Linux.
WINE, can be used to just run Windows Word Publisher, but it is so easy to just load the whole operating system and use both Linux and Windows, sharing files, copying and pasting, etc, etc, without having to partition the HDD.
Yes, you do still have to have virus protection for the Windows operating system, but as VirtualBox copies images (if you wish) these are easy to reinstate if the operating system becomes compromised.
The latest incarnations of VirtualBox work really well.
I also use it on my Vista Business Laptop to run PCLinux MiniMe cause I just love Linux:-)