Having hardware to work quickly is very important especially when adding too much to the project will bring the system down to a halt, no matter what system you are on. Having the best possible system (within budget) is the foundation.
I use Mac OS and I needed a fast system with Nvidia architecture graphics, and after a bit of research I decided to go with a hack-intosh. My system is very low end (entry level for what is possible) and has an i5 processor and 20 inch monitor. Any newer MacBook Pro or desktop equivalent should be sufficient. To see how my system was built visit http://tonymacx86.blogspot.com/search/label/CustoMac
If you can get away with a lower end graphics card, I would recommend a newer laptop for portability, but if you need a higher end graphics card I recommend building a custom system if you have the adventurous spirit.
An adventurous spirit, in this case, means having or learning some basics about computer component install and basic OS setup. It may not be the best option for everyone, but for young people learning creative this can give you an edge and even the playing field with studios that have high end computers that you can’t afford. This is where I found out about the concept: http://nofilmschool.com/build-a-hackintosh/