VT you are also asking for something a bit unreasonable. A computer that can play today's high end first person shooters and strategy games with everything maxed out will based on historical precedence be able to play a game released 5 years from now only on some of its very lowest settings.
PC Top 5 Games of the Year
1. Civilization IV System: 1.8GHz or equivalent RAM: 512 MB Video Memory:128
2. Battlefield 2 Recommended CPU: 2.4 Ghz RAM: 1 Gb Video Card 256 Mb of RAM
3. Call of Duty 2 Processor:1.4 Ghz RAM:256 MB (512 recom)Video Memory:64 MB
4. Grand Theft Auto: San Andreas Pentuim 4 or AMD XP (or better)384MB RAM 128MB Video Card
5. Age of Empires III Processor: 1.4 Ghz RAM: 256 MB Video Memory: 64 MB
Now lets see what they want for recommended systems in 2010.
Starcraft 2: Dual Core 2.4Ghz Mem: 2 GB RAM 512 MB NVIDIA® GeForce® 8800 GTX or ATI Radeon® HD 3870 or better. Amnesia: The Dark Descent: Pentium 4 @ 2.4 GHz / AMD Athlon XP 2500+ Memory: 2 Gb RAM Video Card with 256 MGs Ram Battlefield: Bad Company 2 Processor: Any Quadcore Processor Memory: 2 GB Video Memory: 512 MB (NVIDIA GeForce GTX 260) Civilization V Processor: 1.8 GHz Quad Core CPU Memory: 4 GB RAM Video: 512 MB ATI 4800 or 512 MB nVidia 9800 series or better Mass Effect 2 2.6+ GHz Cure 2 Duo Intel AMD CPU, 2 GB RAM ATI Radeon HD 2900 XT, NVIDIA GeForce 8800 GT, or better recommended
So you are in this case looking at generally double the number of processor cores and about a 30% increase in in processor clock speed, roughly double the video memory and system memory. They also want a more powerful graphic processor with lots more shader cores but I can't in a reasonable space show that, I can just show you roughly 2 generations better of mid level graphics cards. They also want a new generation of Direct X so if your old graphics card doesn't support that new version you are SOL. They also recommend at least one version better OS but you can usually hack/patch your way around that with most games.
In other words most likely a top of the line $1500 system recommended today will run nearly everything (there is always a weird game or two that likes to seriously stretch limits) for the next 2ish years nice and smooth at max or near max settings. It will run most new releases for the next two years after that at average settings. and in the next two years you will be looking at either running on basic settings, running low frame rates, or upgrading your video card for $150 to 250 so you can get back to running a middle of the road settings with your frame rates on some games being CPU limited.
I'm not saying don't build a nice system today I am saying though that a 5 year future proofing plan is a little unreasonable and most likely you would/ will see a better return on your money by spending $600 to $700 as you are going to be able to come close to the same system performance and be able to upgrade your video card at the 3 year mark and still have money left over. You can also simply play with games a year or two old at that point that aren't quite as big of releases and have fu with them as usually right around 18 to 20 months is when the modding and online communities for a game start to reach maturity. (first person shooters are a big exception to this as right around 8 to 24 months is when the hackers on them are at their worst.