Qemu in Debian and Ubuntu are built to use BIOS images from the bochsbios package instead of the builtin ones. Unfortunately, the bochsbios images currently shipped with gutsy do not work with a Windows XP guest in qemu. A comment below states that they do not work with certain Linux distributions either. The current Debian/testing or Debian/unstable packages ship with a more recent BIOS and work fine. So all that's needed to fix this bug is a backport from the development version of Ubuntu.
Original bug description below:
> Binary package hint: qemu
> After updating to gutsy, qemu doesn't want to start an XP instance. I tried with Damn Small Linux (from the CD ISO) and it works flawlessly.
> It fails during XP's boottime. The qemu windows hangs up and can't even switch to the qemu's console.
> I checked by downloading the source code (the "vanilla" code), compiling it and running.. and found it works (with the same XP image).