I'm confused too but so far I've been lucky all the parts work well together.
You need a friend who could advise you on the technical bits and macth them to your need.
All I know is to get a good motherboard and if you could an all solid capacitor one for enhance longevity.
Get a harddisk that's has a high rpm and the capacity to suit your need. For gamer it's better to get larger than 500Gb of hard disk.
As for memory since you're planning to use a 64 bit system having more than 4Gb of memory would not hurt though it may not be that useful to have ridiculous amount of memory since there's no app that's going to even need 8Gb of RAM anyway. DDR3 is the newest typer of RAm out there. If you're planning to use DDR3 make sure you buy a motherboard which supports them. There's timing in RAM too the faster the more expensive they become.
For processor I just think i7 a waste of money but if you have the extra cash well why not. A quad core is the minimum and try to avoid dual core nowadays.
Most important of all never ever buy a cheap PSU(power unit). Buy a good one and buy one which is rated higher than what you need.(if your CPU is going to need say 650Watt supply use say an 800Watt PSU or higher so you wouldn't tax the PSU unit too high of its rating and get a more stable power fed to your system).
Good luck and congratulation on your new system when they come together. Buying branded CPU is a ripp off imo
. I like it more when you can choose what you want inside the tower yourself and they come much cheaper too.