A laptop DJ first needs a laptop with a fast enough processor to handle a mixing program and enough memory to hold thousands of songs. Depending on what you want to accomplish as a laptop DJ determines what kind of equipment will be required. There are many DJ programs that are simple to use and mix songs seamlessly. More advanced programs are capable of record scratching, mix recording and video synchronisation.
A Macbook Pro is the most commonly used laptop with DJs. The Mac operating system is the most dependable for running the programs used by a DJ. Some use a PC laptop instead of a Mac, it comes down to personal preference. A reliable laptop has at least a 2.4 GHz processor and 4 gigabytes of memory.
There are many programs that turn your laptop into a set of turntables. Serato Scratch Live, Traktor DJ, Reaktor and djay 3. Djay 3 takes your iTunes music and brings it into a mix list in the program to choose from. There is also an auto-mix option which allows you to enjoy the party while the program automatically selects songs from a playlist and mixes them. If you are looking to have more control of your mixes then advanced programs like Serato Scratch and Traktor are what you are looking for, which allow multi-track mixing and sampling.
Whether you are the DJ for a house party or a club, a sound card is required to ensure a good performance. Pre-cueing with a set of headphones isn't possible without an external sound card and there are several options that will produce rich, powerful sound. The Maya 44 USB has two pairs of RCA inputs, the Numark DJ I/O is simple and affordable and the Indigo DJ card has high quality sound and performance.
Controlling the EQ of your mix is difficult without a USB controller. USB controllers plug directly into your laptop giving you easier control over EQ, cross-fading and scratching. Numark's Stealth Control is built for heavy use and offers five faders, the Hercules DJ controller is an all-in-one that is very affordable and the Vestax Spin DJ controller is designed to work specifically with iTunes.
If you already have a reliable laptop, lots of music and a desire to make people dance then you are half way there. Many DJ programs offer free trials, so explore some options to see which suits you best. Tutorials on laptop DJ-ing are all over the internet to get you started spinning. With a couple hundred dollars and some time to practice you can be rocking the next dance party.