quadcore with 8Gb of ram and a 100Mb connection will run 200+ players smoothly with no issues
hard drive doesnt really matter tbh, and in reality the quad core doesnt do much for the server, as it will only run on one core anyways, the database however will use all the cores depending on how you have it setup, and the database is the resource hog
as far as the hard drive, i would get 2 of them, have all ur DB backups save on the secondary hard drive, and only back up every hour for 1-2 weeks, otherwise your hard drive will fill up really fast, but dont keep backups on the main drive as this will lag you out pretty fast, 160Gb will be fine for this
get a good sized hard drive for your main, as the LogFiles will build up after time, and eventually will take the entire hard drive over, best thing to keep that at bay is to go in at the end of every month and put all the logs into a rar file, this will allow you to search thru your logs easily, and if u have to go back a month, u have them all in compressed files which will take up much less space then leaving them there, and its easier to keep all the logs organized by naming them by month and year. 500Gb+ will be fine for this.
some ppl also like to get some stupid amount of bandwidth (like i did in the beginning lol) but as it turns out having 250-300 players on all month you wont even use 600Gb a month, so dont go overboard on that, all u will do is throw your money away.
and nvr host downloads on ur server, this is the single most thing that will cause your server to lag, because more bandwidth is used by 5 ppl downloading at max speed for an hour then 100 players will use all week, which means if there are 5-10 ppl downloading ur client from the server, everyone on will get the worst lag spikes, pisses everyone off, just dont do it lol.
dont overkill you DB version either, sql 2005/2008 is just retarded to use, it will suck the resources right out of your machine, and doesnt run the game any better than sql 2000 w/sp4, plus they are harder to use then 2000 is, im sure they are more powerful than 2000, but if you put a viper engine in ur pinto, you still just have a pinto . . . .
and, less is more in most cases