Kattus: Ok, if I update my PC to todays standards which components I should buy to get decent performance?
Processor... Display card... etc... etc...
This has been suggested on one place:
Intel Core i5-750,
Gigabyte Radeon HD 5850 1 GB, PCI-E
MSI P55M-GD45
2 GB, 1333 MHz DDR3
Do you HAVE to use windows 7 on PC with new components. Is it possible to use XP?
i5 750: is it cheap? If prices are like in the US, the total system cost for a decent SB will only be slightly more. The main advantage to Nehalem, right now, is cheaper overclocking, but a 750 aught to be awfully close to a 2500(K) in price.
If you do not plan to overclock, the 2500 and 2500K are interchangeable, as are motherboard chipsets for socket 1155. IMO, going AMD would be a better way to shave costs v. Sandy Bridge, than going with Nehalem, should that be the reason for the i5-750.
HD 5850 1GB: the prices are right. It is hard to go wrong with a GTX 460 1GB, HD 5850, or HD 5870. The HD 6850 is a decent bit more power efficient, but has no other real advantages over the 5850. IMO, get an MSI Hawk, or a Sapphire VaporX, if you can, for the sweet coolers and otherwise good quality. Price may rule those options out, however.
Mainboard: this is CPU dependent. Changing to S1155 would change available options, as would going with AM3.
* USB 3 could be handy to have on the board, particularly if it is a microATX.
* SATA 6Gbps, hyped on every motherboard's feature set, is patently useless for 99% of users. Of the leftover 1%, most of them find it useful as an e-peen, paired with a fast SSD, and don't take any real advantage of it.
* If you get Windows 7, before the install, go turn AHCI on for all your SATA ports. Windows quietly enables several useful features, if you install the OS with AHCI already turned on, notably NCQ, which makes quite a difference in Win7, and hot-swap, which you may very well never use. It can be enabled later, but it is easier to have it from the beginning.
2GB RAM: 4GB, as 2x2GB, minimum. RAM is way too cheap not to, and using more than 2GB is very easy to do. Make it a point to get 1.5V rated RAM, too. Never, ever, ever, EVER skimp on the amount of RAM, if you can afford it. Note that if you stick with a 32-bit OS, you will not be able to use more than 2-3GB, as any devices that use DMA start taking up address space, and your video card's RAM tends to be included in that.
OS: you may use XP, but you will lose out on DX10 and up, will be limited by RAM, and XP support ends in 2014, which could be within the useful life of the PC. Typically, you will see software you want that does not support it within a couple years of support ending. XP got treated special, because Vista was a turd, but as 2014 approaches, don't be surprised if it gets to be problematic. I would get Windows 7 64-bit, and keep a 32-bit XP box for games that flat will not run in 64-bit.
Not mentioned: an affordable PSU for such a system, if not overclocking at all, or not much, would be pretty much any of Corsair, Antec, or Seasonic's 400W to 500W units. Go with 500W, or a bit more, if overclocking. Don't get too cheap of a PSU. As affordable as Corsair and Antec units are, these days, there is no excuse for getting a crap PSU for a nice system.