Say again s l o w l y,
With 29Gb Free on a 40Gb HD, you do not need to worry about freeing up space. I would not worry about it. If you install and uninstall programs regularly, all you need to do is defrag every so often. If you are not installing programs regularly, I would not worry about defragging unless the computer slows down.
Windows, especially WinXP Pro, has a very good set of utilities built in to the OS, so no need for third party programs like NSW.
I try to install the very least amount of programs needed to do everything I want on the computer.
I checked and the Trojan, ByteVerify, is a non destructive virus, so you should not have any ill effects from having it in your system.
Take Care,
Richard