$900 gaming MicroATX rig

I'm ready for an upgrade, my computer specs now are

2.6ghz Core 2 duo
2gb DDR2
640mb 8800 GTS
550 watt PSU

The reason I'm upgrading I'm tired of playing games with low res 1280 by 720, I want to play at 1920 by 1080.

Even if i put 4gb in my system, i still wont be able to run New FPS games at 1080p right?

Let me know if my new build will do the trick.

3.4ghz quad-core (non over clocked)
4gb DDR3
1gb 5850
750 watt PSU

Or do you think I should wait for Fermi Nvidia and or use a Core i5?

CPU - Intel i5 750 (best bang for buck CPU for gaming, overclocks well)
RAM - 4g DDR3 is fine, 1333-1600 Mhz+
GPU - HD5850, great card, if you do get this you will want to get a 8x8x Crossfire capable motherboard, this will make your system much more future proof, Gigabyte GA-P55M-UD4 Motherboard for example. (8x8x is only a 4% performance loss from 16x16x despite it being half the value)
PSU - 750w should suffice, but remember - dont cheat on getting a cheaply made psu, go for a corsair or other reputable brand, 80% effiency at least. I recommend you get a samsung F3 HDD, a crappy HDD is a great way to slow down a good system.

As for fermi, wait for it if you want, though the system specified should run all of todays games fine, if not in the future get another 5850 and crossfire it.
Also remember that gaming relies mainly on the GPU, not so much the RAM or the CPU.

yes, msi's p55 mobos are excellent, what case do you have?Edit: the msi isn't matx

All looks good, maybe get a samsung F3 HDD, apart from that GL with the build.