There are many programs for creating and removing partitions. Most operating systems have their own, and it can be a good idea to use each operating system's own, just in case it does something unusual that the others can't. Many of the programs are called fdisk, including the Linux one, or variations thereof. Details on using the Linux fdisk are given on its man page. The cfdisk command is similar to fdisk, but has a nicer (full screen) user interface.
When using IDE disks, the boot partition (the partition with the bootable kernel image files) must be completely within the first 1024 cylinders. This is because the disk is used via the BIOS during boot (before the system goes into protected mode), and BIOS can't handle more than 1024 cylinders. It is sometimes possible to use a boot partition that is only partly within the first 1024 cylinders. This works as long as all the files that are read with the BIOS are within the first 1024 cylinders. Since this is difficult to arrange, it is a very bad idea to do it; you never know when a kernel update or disk defragmentation will result in an unbootable system. Therefore, make sure your boot partition is completely within the first 1024 cylinders.
Some newer versions of the BIOS and IDE disks can, in fact, handle disks with more than 1024 cylinders. If you have such a system, you can forget about the problem; if you aren't quite sure of it, put it within the first 1024 cylinders.
Each partition should have an even number of sectors, since the Linux filesystems use a 1 kB block size, i.e., two sectors. An odd number of sectors will result in the last sector being unused. This won't result in any problems, but it is ugly, and some versions of fdisk will warn about it.
Changing a partition's size usually requires first backing up everything you want to save from that partition (preferably the whole disk, just in case), deleting the partition, creating new partition, then restoring everything to the new partition. There is a program for MS-DOS, called fips, which does this without requiring the backup and restore, but for other filesystems it is still necessary.