Since you are interested in going with a gaming system here are some suggestions:
Motherboard (mobo):
ASUS or GigaByte. DFI and Intel both make good mobo's. ASUS is tops in my book. On the mobo go with Socket 1366 since it's the latest and the greatest. Make sure it's an Intel board and not an AMD board. Also make sure the form factor is ATX. Now with the ATX Form Factor you need to find a case that supports the ATX sized mobo since there are other sized mobo's. Micro ATX, mini-ITX, XL-ATX. The standard ATX form is the most support version so you're better off sticking with this.
Case:
ATX Full Tower or ATX Mid Tower
Processor:
Intel
Quad Core - Intel Core i7 3.2GHz
Six Core - Intel Core i7 Extreme Edition Gulftown 3.33GHz
RAM:
For the Socket 1366 mobo I'd look at the DDR3 1600 as a minimum
Video:
DVI or HDMI only and I'd make sure the card I got was SLI. I'd get one that interfaced with either PCI Express 2.0 x16 or PCI Express 2.1 x16
Power Supply:
Minimum 700W or higher. If you are planning on running dual SLI video cards then I suggest getting in the 900W realm.
CD / DVD Burners:
Stick with the SATA drives only. Not only are they faster than the IDE type but the IDE is old technology and you have to deal with thos wide ass ribbon cables. Whereas the SATA cables are significantly thinner which helps your air flow inside the computer. This in turns in helping you keep your system cooler which gives your system longer life.
Floppy Drive:
nix this drive unless absolutely needed. I suggest getting a nice internal card reader.
Fan/Heatsink:
Needed to cool your processor. I personally like the direct cooling where the fan points directly to the processor but they do offer indirect cooling as well.
Thermal Compound:
Make sure you put some between the heatsink and the processor. Usually the new heatsinks come with compound on it but I wipe it off since I'm not satisfied I get enough coverage.
Hard Drive:
Western Digital, Seagate or even Hitachi. Stay away from Maxtor drives, they are typically pieces of junk. The drives come in different interface styles. IDE, SATA, SAS and SCSI. Whatever your choice stay away from the old IDE interface. Again it's slow and outdated. What ever you go with make sure your mobo will support it.
Cooling Fans:
Whatever you do with this, you can NEVER have enough cooling fans. Check the case you choose since they sometimes will come with only the rear fan or none at all. I get my cases that offer top, front and side vents that allow me to mount my fans. Most of our office computers have at least 4 case fans and this does not include the processor fan.
Operating System:
In today's time most are moving into the 64bit realm. I suggest doing this but in many occasions many old software packages you're running in XP or lower will not run or require updates. If you have a printer older than 3 years you might get lucky and find updates for the printer or download firmware updates. Chances are you might need a new printer.
There's a good bit to think about when building a system but when your done and it boots up and purrs like a fine engine it was all worth it. Also you can usually save some money doing it yourself.
Lastly if you are looking for some deals and good prices to build your system you can always visit
NewEgg. This is where I've been purchasing my parts for about 4 years. Look under the Computer Hardware tab to start your adventure.
Hit me up if you ever have questions or need guidance.
Good luck.