The problem there is that the root and possibly swap partition for ubuntu are sitting inbetween where those would have to be moved to the rear of the drive first. That is time conuming.
Once moved the unallocated drive space not actually any partition is easy to fill by simply resizing the XP primary with the option seen with GParted. That only takes about a minute or so in comparison.
A second and third set of alternatives if you have no plans at running ubuntu or any other Linux distro would be deleting any for ubuntu and simply expanding the XP primary to fill in the drive as a large single primary or grow the XP primary to a certain point and see a second storage partition created for storing and backing things up.
At present you can simply grow the XP primary somewhat by moving the Linux partition(s) and creating a new one for storage to still retain a working dual boot. These are the options available unless planning a clean install of Windows for your own use there.