you want a PC? you should build it yourself. its cheaper and lets you buy exactly what you need.
first you should decide/find out a budget. i dont know it, so i will assume ~ £600, enough for a good pc
for supcom a cpu with a clock speed on 3.0 per core will be fine.
intel i5 or intel i7 will do, but intel i5 is usually better for gaming becuase it has higher clock speeds, but it has no multithreading (4 "cores" not 8) so an i7 is better for rendering and things that can use all the cores of a cpu and not just one.
its very important to note that you can get a REALLY good deal with some AMD cpus. they are about as good as intel ones, but 30-40% cheaper (intel: £220 AMD:£150). if your budget is not huge then i would recommend going this way.
example:
http://www.overclockers.co.uk/showproduct.php?prodid=CP-372-AM&adword=google/pla/unoptimized&gclid=Cj0KEQjwo82eBRCR1Yr2u-G-sK8BEiQAbrSjVCOFgkxu8-SWEHaDDBezIMPmiMOMcuF-EsDSjtz5x80aAiIx8P8HAQ(cpu about as good for gaming as my intel one for £100 less)
RAM is also important for FA as it turns out:
http://hardforum.com/showthread.php?t=1709516check the frequency of your ram before you buy it, 8gb should be more than enough. (i have 6gb) if you ever need more you can get that later (maybe in 3 years) anyway.
faster ram is usually better.
make sure it is DDR3, thats the type of slot it fits, if its not, you wont be able to put it in to the pc.
graphics card: this one is a hard choice because it depends a lot on what you want to do. if you want to only play supcom then a mid range gpu will work quite well. but if you also play new fps or render then a good one is important. the main choice here is between AMD and nvidia. from there on, its a price thing.
note: i have had personal experience with AMD GPUs and can say the are quite good but are fussy with drivers. if you want to run linux, beware. if you are unsure, pick nvidia.
motherboard
im not a specialist here, but once you know what type of cpu you want, you can check the cpus socket, and then find a matching motherboard for it.
bear in mind AMD and Intel motherboards only work with cpus from that company
getting an amazing one is not important, but a very cheap one is also bad. check what slots it has and make sure it has what you want.
then check that all the other components have the right slots to fit in. unless you pick a really old component, they should all have matching standards.
power supply:
every component has a wattage. add them all up then buy a power supply that can handle it. to be on the safe side, always buy more wats than are needed, but not 1200 if you need 500
case: check the size standard on the case for the motherboard: (atx, mini-atx, micro-atx) and make sure they match. make sure the case is big enough for the psu. everything else should fit, but if you want a small case then better make sure.
screen:
1920x1200 resolution and then pick the cheapest, if you budget allows it, you can go for a better screen, but this is the minimum for me.
keyboard: i dont find this important at all. one for £30 is more than enough, i have one i found somewhere :/
mouse: actually helps, a good mouse is important. but not so much for supcom. i recommend to try it before you buy
if you are unsure about what you are doing, you can always post a list of your components here to check.
also this helped me:
http://uk.pcpartpicker.com/hope this helps.