In order to lengthen the lifespan of my machine I am replacing the weakest link, the hard drive and installing a new OS.

I had planned on using xp pro as my virtualbox host and ubuntu as guest.

After messing with ubuntu desktop and server I am really impressed and am thinking of reversing the virtualbox setup; ubuntu host xp guest.

I would use XP for Adobe Fireworks, Netflix, and iTunes (maybe) that's pretty much it.

Any reason not to do ubuntu host with xp guest? I know the xp vbox will run slower as a guest but really how much slower?

It's a desktop. 4gb ram, 500gb disk, Pent D 3.2 ghz