Hi Bob,
To be honest, any modern SATA HDD will do for CFS2. If you can afford a 7200rpm speed version then that will give you the best access times, which will keep things to an optimum.
( For info - a basic install of CFS2 is only 858Mb! I run a basic version off a cheap memory stick for fun, which runs very well.)
The rest of it is common sense and applies to all computers for personal use:-
Keep your system 'lean and mean', don't add or install cr*p. Be discerning about what you put on the machine, and what programmes you really need to have running all the time.
Good husbandry of the pc, ie have a good freeware, low-resource hungry, anti-virus i.e Avast, AVG or M$ Security Essentials (please don't use uneccessary, expensive, resource-hungry anti-virus progs such a McCaffee, Norton 360 and others), fully un-install progs, run defrag once a month (M$ defrag is not that good, something like Defraggler and others are much better at it, but the standard one is free and comes installed), be careful about updating all the hardware drivers, with just a thought of 'if it ain't broke, don't fix it'.
Keep the pc physically clean and cool. Turn off at night so that the RAM is cleared, and you will have the max RAM for use the next time you fire up the pc, this also allows the pc to cool and electrically de-stress by discharging.
Hopefully you are going to an independant computer store, if so, they will know and understand. The biggies such as Pc World etc, will not have that personal service.
The requirements of CFS2 are very low, the add-ons and mods are what causes your computer to work harder, so again keep your CFS2 installation tidy and ordered. You can aliase sounds, panels, almost everything, to cut down size, but that will not really affect speed or frame rates.
All these things will help keep you pc running to it's optimum, and give it a longer shelf life.
Hope this helps
Cheers
Shessi