dual OS

[robxyz]

i want to install xp on a computer running ubuntu; is that possible?

[mushwars]

yes, if you haven't installed ubuntu yet and you have xp you can resize it using the install cd then you can add ubuntu (best option)
alternitivly if you have not installed windows yet (going to be harder) you can either use virtual box and install it or you can try resizing your home partition, however if your home partition is not sda3 (the last partition) (i.e. you would have had to partition it yourself because the ubuntu partitioner does weird stuff) then you can resize the ext 3 and add an ntfs ( this is all together a bad idea) if you have only ubuntu now install windows stuff with wine or use virtualbox it is now too late to install windows on a new partiton unless you didnt format your entire drive.