[Taqwus]

Last I checked, Linux could read NTFS partitions pretty well, but writing might still have been considered unstable. Haven't checked for a long time.



Generally speaking, it's fine to keep existing partitions -- although having one partition free would be a rather good idea; while you can install at least some Versions of Linux into a FAT32 filesystem, for instance, it's not too advisable. Better to keep it separate. A swap partition is also a good idea. If they take up your entire drive currently, you may want to look into partition-resizing software and whether a given distribution comes with any.
The usual bootloaders available (lilo, grub, others) are pretty good at letting you select which OS you want to boot from at start.