Yes
No.
Yes, you can run linux on XP without partitioning. There are liveCDs, which are bootable cd(
http://www.frozentech.com/content/livecd.php), as well, Look into qemu (there is a linux distro called DSL embedded that will run right inside windows.
http://ibiblio.org/pub/Linux/distrib...small/current/ and download the dsl-embedded zipfile. You can also modify the batch file to boot any linuxlivecd.)
as for partitioning, you can repartition, howver, most likely you will need a third party tool such as partition magic.