On January 1st 2009, the latest version of windows virtio network drivers was released supporting Windows XP, windows 2000 and windows 2008. The release is in the form of an iso so you’ll have to mount as a virtual cdrom for installation. The procedure for upgrading the virtio drivers can be found on a previous post found here: Upgrading Windows Virtio Drivers. After upgrading your drivers, the version should be listed as 5.1.2008.1229 as shown in the snapshot below on a windows xp guest. Enjoy!
The latest drivers can be downloaded at the following link