Did you already buy that video card? If not I'd advise you to get the Radeon 4850, it's better and in a similar price bracket, it's cheaper actually, if I remember correctly.
Just to get you started.
CPU: Intel Core 2 (whatever), they have so many damn models now of their Core 2 Architecture that I don't even keep up with it anymore, just find a processor that you like whose cost is in reason. You can use Newegg.com to browse for one, same with all the other components you'll need to purchase.
Motherboard: If you go with the Radeon 4850 solution that I provided above then you'll want a nice LGA775 socket CrossFire compatible motherboard, otherwise, if you're sticking with the 9800GTX you'll want again an LGA775 socket motherboard, only this time you'll want it to be SLI compatible.
RAM: How much RAM you get depends on your budget. If you've got the cash go for 4GB of RAM, whether it be 4 individual sticks packing 1024mb each or 2 sticks packing 2048mb each, really depends if you plan to upgrade even further (not advisable). Or you can get a 2x1GB set, which should do fine too, anything less isn't advisable when running Vista, which I'm assuming is going to be the OS you go for.
Hard Drive: Hard drives are getting cheaper and cheaper nowadays, you can easily find a 750 GB 7200.1 RPM hard drive for 100 dollars nowadays. Notable companies are WD, Hitachi and Seagate, the size of your hard drive is based on your taste and needs.
Power Supply: This is an important component and you really can't afford to get cheap on this part of the computer. You'll want a sturdy 700W+ power supply (It's a bit much, but more power isn't a bad thing). Good companies are FSP group, Corsair, Silverstone, OCZ.
Optical Drive: Up to you, all CD drives are more or less the same now, you'll likely want a DVD+RW drive unless you intend to go for a BluRay disc solution, which probably isn't advisable seeing as how prices for this hardware component are currently dropping.
Case: It's up to you again, depends on what you find visually appealing for you, cases are more or less the same, the only way you can differentiate a good and bad case is air flow and its ability to contain noise, otherwise the other details of a case don't have much of a bearing on your PC experience.
OS: You'll need to buy an operating system, depending on what you need, the most suitable versions of Vista for you would be Home Premium or Ultimate. Linux is an option, but seeing as how you're building this expressly for FarCry 2 it wouldn't be ideal.
I could've been more specific and actually picked out parts for you, but part of the PC building experience is finding parts on your own. If you decide you need more specific help though, just ask. Someone will probably post up a list for you within the next 10 minutes or so anyway
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