I'll explain how I did it - it's much easier to understand from an example.
First of all, I used fdisk so I could know which were all the partitions in my system and what they were called.
debian-indraprastha:/home/anirudh# fdisk -l
Disk /dev/sda: 40.0 GB, 40060403712 bytes
255 heads, 63 sectors/track, 4870 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 * 1 1912 15358108+ c W95 FAT32 (LBA)
/dev/sda2 1913 3960 16450560 f W95 Ext'd (LBA)
/dev/sda3 3961 4870 7309575 83 Linux
/dev/sda5 1913 3187 10241406 b W95 FAT32
/dev/sda6 3917 3960 353398+ 82 Linux swap / Solaris
/dev/sda7 3188 3916 5855661 83 Linux
Now take the first entry. That partition is called /dev/sda1 and is the C: drive on Windows. Now I use the mount command to mount the partition. Mounting means that I attach a physical device to a directory, so that the directory itself becomes the device. It's a concept that you get used to once you are familiar with all this. To mount the partition, I need a mount point. This is any directory that I create.
debian-indraprastha:/home/anirudh# mkdir /disks/c
Now I mount /dev/sda1 to /disks/c
debian-indraprastha:/home/anirudh# mount /dev/sda1 /disks/c
You can check if it has been mounted using the df command.
debian-indraprastha:/home/anirudh# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/sda3 6.9G 4.7G 1.9G 71% /
tmpfs 253M 0 253M 0% /dev/shm
/dev/sda5 9.8G 7.9G 1.9G 81% /disks/d
/dev/sda7 5.5G 4.6G 702M 87% /disks/s7
tmpfs 10M 716K 9.4M 7% /dev
/dev/sda1 15G 13G 2.4G 84% /disks/c
See the last entry? That shows that /dev/sda1 (the C: drive) has been mounted on /disks/c. Its total size is 15 GB of which 84%(13GB) has been used and 2.4GB is available.
Now there's a file called /etc/fstab that comes in very handy. This mounting business is temporary. It gets "unmounted" after I shutdown. I would like to automatically mount it each time. I do that by modifying the /etc/fstab file. The /etc/fstab file keeps static information about the filesystems(refer $man fstab). Another file that comes in handy is /etc/mtab. This file keeps info about all the devices that have been mounted. After I mount /dev/sda1, an entry is made in /etc/mtab automatically.
/dev/sda1 /disks/c vfat rw 0 0
Now I copy this line into my /etc/fstab, with some modifications.
/dev/sda1 /disks/c vfat auto,exec,rw 0 0
Now each time the system boots, that drive will be mounted automatically.
Now, suppose I don't want it to be mounted now? I use unmount.
debian-indraprastha:/home/anirudh# umount /dev/sda1
To disable the mounting of the paritition automatically, just remove that particular entry from /etc/fstab or uncomment it.
Have fun :-)