This is one part of Linux which is still is considered a curse. To partition a hard disk you not only need knowledge, but also a lot of experience. Remember: any mistake can cause irreparable damage to the data in your hard disk. I suggest that you back up all your important data beforehand and preferably have a computer guru alongside you.
Before we start we need to know what is a hard disk. How can we store such large amounts of data? Five years a hard disk could store barely 600MB. Now 20Gb is common. A hard disk is made up of glass or special optical material. A head, which hovers above the platters, reads and writes data to the disk. One hard disk is partitioned into two parts viz. the primary partition and the extended partition. The extended partition is divided into a number of logical drives. If you have only one drive showing in windows (e.g. c: drive) then it is likely that you have only one partition.
One of the biggest myths about Linux is that it requires a separate hard disk. This is not so. What we require is a separate partition. The latest versions of Linux can install in Windows itself.
Make one of the partitions on your hard drive empty of all data. This partition has to be formatted in the Linux format, which is different from Windows. We delete the partition to create free space.
Requirements for partitioning for Linux:
A partition, which has approximately 1 GB free. There should be no data on this drive, as we have to convert it into free space. Minimum installation for Linux is around 150MB (of course you can do it for lesser. A full-fledged minimum install does take 150 MB). Typical installation does take 400-500 MB. Max install with all applications can go up to 2GB.
A disk partitioning software like Partition magic, fdisk, and disk druid etc.
A fair amount of courage.
All your stuff backed up into some other HDD or written on a cd.
At the DOS prompt, type fdisk after rebooting into Dos. Enable large disk support. A menu will come up. Choose option three, which says, "Delete a partition". Delete the empty partition. This creates free space. Be very careful not to delete the other partitions or make any other changes.
This free space is the raw material, which is necessary for installing Linux. The next part will be to format it in the Linux. This will be done during installation, which will be done next time.