The only way to learn is by experience and trial and error my friend. I hate going into the innards of my computer because I fear everytime it just won't POST like it should and this is for changing out things like fans! BUT I'm paranoid like that.
First off, that particular motherboard and chip you're planning on getting IS expensive..thats high end stuff right there. Might as well go for it because building a PC isn't hard especially if you read like you said you've done.
I would suggest getting this board instead:
Its the MSI "K8N Neo2-FIR" It has the VIA chipset instead of nForce cause trust me VIA will be better. There will be atleast a couple of people to back me up on that. Beyond that..on the platinum...the North Bridge fan will interfere with any high end graphics card you may decide to put in in the future. You say you want the eVGA(eVGA is an excellent choice) so yeah you'll definitely want to get the K8N Neo2-Fir instead of platinum cause you'll have a ***** of a time fitting that 6800 in the AGP slot. I'm sure they probably thought of it somewhat...but it just looks WAY too close to that North Bridge fan. But like I said I also suggest that other board because of the chipset it has. Should offer good stability. The Dual Raptors are a good choice, but that is SATA and setting up SATA drives and depending on if you want a RAID-0 or RAID-1 setup will take further reading and will be more difficult to setup than a normal standard western digital 7200 RPM IDE drive. Your ram is a good brand a gig kit would be a good start....at this point going from a gig to 2gigs you wouldn't notice that much of an increase so a gig is good. Make sure you get high performance mushkin ram though and not just their value ram. For the system you're out to build you definitely don't want value ram.
Make sure you have a nice STRONG power supply to power all that cause those 6800 cards suck a lot of power. Here's a decent link for wattage calculations:
and here's a link to find out approximately you have running per rail (meaning +3.3v, +5v, and +12v) You can have an 800w power supply but if you only have a 10a rated +12 rail you'll be screwed. So look for a strong +12 rail cause thats what your HD's, case fans, motherboard, and DVD-roms etc...run the most off of...your processor sucks the most out of the +12v rail too. Here's a little older site that'll show you how to calculate your totals per rail. Like I said its a little older but it'll still give you an idea on how to choose a good power supply based on rail needs.
Building a PC should be fun an exciting and generally is. The only thing in your case is the SATA Drives...those will be fun to set up =) cause that requires something completely different than just tossing in an IDE drive and the winXP CD. with Dual raptor drives you should create a RAID-0 which I believe (unless I got 0 and 1 mixed up) will be a little slower cause what it does is mirror the other drive...so incase one goes down you have a perfect duplicate that can come in right as the other one fails...on the otherhand..if you have RAID-1 and just have it as a storage and backup..then loading of windows and copying files should be fast as hell for you.
You seem like you're ready to build your own PC and you have all of us here to help you out. I would say GO FOR IT!