Adding a second drive is one of the easiest upgrades you can make to a PC. Generally, you don't even need to enter the BIOS at all and all you need is a screwdriver.
First, look at the specifications for your computer's model and determine whether it supports PATA(IDE, most older PCs and many newer ones support this,) SATA2 (supported by almost all PCs since 2007 or so,) or SATA3 which is all the new hotness and is supported by most newer PCs. It's not uncommon for a computer to support all three interfaces, though an off-the-shelf model like a Dell is less likely to support more than one. Given the choice, you should opt for SATA3, since it's the fastest followed by SATA2 and finally PATA.
If you computer supports only PATA drives, then you may want to look into getting a SATA controller card. These are expansion cards that plug in to a PCI card slot and provide one or more SATA2/3 ports. If you go this route you may need to install the SATA controller card's drivers before installing the drive itself.
Once you determine the type of drive you can use, you can simply pick one of the many, many models of hard drive that are available for each type. Bigger drives are obviously better than smaller ones, and faster RPM drives are better than slower RPM drives; a good target is 7200RPM (assuming you don't opt for an SSD, which has no moving parts at all.)
After getting the drive, all that remains is to install it and set it up. Installing is very simple as all you need to do is connect 1 cable to the motherboard and 1 cable to the power supply (and secure the drive with screws, of course.)
You may need to set a jumper on the hard drive to enable or disable certain features, the manual with the drive will explain the different options and provide a diagram for reference. Jumpers are small metal pins which form part of a broken circuit. Jumper covers are small plastic and metal sleeves that fit over two jumpers to complete the circuit and thereby change a particular behavior of the drive (notice the small black square of plastic the finger is pointing to):
You can then boot your computer; Windows ought to detect that a new drive is installed and install the appropriate drivers. Once that's done, you can go about partitioning and formatting the drive
. It will then be available like any other drive, or if you partitioned it into more than one volume, like several drives.
And then you're done with the installation. Now you get to move all the files you want over to the new drive.
As to improving performance (i.e. speed) there are only a few potential advantages to installing a second hard drive.
First, you can configure Windows so that it has a large pagefile (2-3GB for most systems) on the new drive (preferably on its own dedicated volume) in addition to a smaller page file on your main system drive. This allows Windows to read/write the pagefile while also reading and writing to the system drive. The performance boost isn't going to be spectacular, but definitely measurable.
A related tweak would be to move as many programs as possible off of the system drive (that is, out of C:\Program Files) and onto the new drive. This has the same benefits as moving the pagefile: Windows can read and write to system files while simultaneously reading and writing to the application's files, since the two sets of files are physically independent of each other.
If you have a version of Windows newer than Windows XP, you can use NTFS symbolic links to move entire directory trees from one disk to another while leaving a symlink in the original location (symlinks are like shortcuts on steroids. I used a symlink to move my entire Steam games directory to another drive without having to reinstall.) For Windows XP symlinks aren't available but (I think) you can mount a volume as a directory under another volume to achieve the same effect with NTFS hard links.
Probably the single biggest performance boost would be brought about by buying an SSD drive and installing Windows on it, relegating your current drive to secondary status. This would also be the most labor-intensive idea and may be further complicated by the fact that OEM versions of Windows (like those that ship with Dell computers) are usually tied to the original hardware; reinstalling using your OEM CD and product key may fail if you swap out the original drive.
Edited by Andrew, 02 February 2012 - 04:54 PM.