advice is ok BUT make sure you fully understand what you are going to do and have a print out that you can follow.
You dont say what size your disc is but process is slow if you have a large drive (anything over 10gb)
If you have partitions on already and you are wanting to start again from scratch then you must remove the partitions in the reverse order they were created.
eg if you have your drive partitioned as c drive primary then two logical partitions in the extended partition (d, e) you remove e, then d then remove the extended partition then remove the primary (c).
FDISK allows you to enter % of disc space rather than entering mb size.
You can achieve the same thing using support system disc from disc manufacturers eg maxtor, think it's called maxblast3. here you can remove all data wipe disc completely clean, paretition etc all very easily. Again it can be slow for instance my 80Gb drive needed to be completly wiped not just reformat, took over 6 hours!!