Your friend seems a bit weird.
From what you've told me, he wanted you to build his system. Then all you did was give him advice on what to stick in there. He decided not to take your advice.
So then he picks out his own gear for the rig, but has his friend Aeron put it together for him. Then he doesn't remember what parts he put in there, and furthermore requires your help to make the OS/software run faster.
Dude, that's just a confusing story LOL
It seems to me that if he can pick out every component that goes into the machine, there would be no need to have someone physically build it. If you got all the parts, just start snapping them into place. The only tricky part might actually be spreading the thermal compound, and hooking up all the PSU connectors. I haven't built my own computer, but I probably will in the next week or so. And to be honest, those are the only two things that intimidate me. But the Mobo manual should be pretty clear on where to plug the PSU connectors.
It just seems weird to me that this buddy of yours needs your help tweaking the OS and software to make his computer run faster. I'd think as a rule of thumb, if you can't figure out "RUN – MSCONFIG" and cancel the unneeded 30 programs that load up on start, than you got no business trying to build a computer. I mean, you'd have to have a little software knowledge to build a computer; like taking a blank unformatted hard drive, popping win98 startup in the floppy, format the HDD, then pop in your OS (assuming this is not an Apple). Actually on newer computers I doubt you'd need a floppy boot disk to setup a partition. My comp won't boot from the CD.
Also, I have a policy when tweaking someone's computer: I typically don't!
Years ago, for my mom, my neighbor, and my mom's neighbor, I tweaked their computer (cancelling unneeded startup crap, defragmenting it, setting their CRT refresh rate to something other than 60Hz, temporarily installing and running a few different malware detectors, turning off all the sound effects and visual effects and the massive BMP desktop background image).
After doing these simple things their computer ran at nearly twice the speed. Boot time went from about 7 minutes to about 3 minutes and so on. But then they did nothing but complain about it: "where's my desktop wallpaper? How come all of my instant messengers aren't loading at startup? What happened to all the sound effects?"
I then had to explain it was all of these things being loaded up and put into memory at startup that was the majority of the computer's lag. But apparently they wanted all of these useless things. And lord, they wanted that 1MB background image so bad on their desktop.
And of course, if anything goes wrong with the computer a week later, your phone will be ringing and they will be asking "What's wrong with my computer? What did you do to it?" And in nearly every case what the problem is has nothing to do with what you did. But still, that error message wasn't there until a few days after you worked your magic on the computer, so it must be your fault. And the statute of limitation on how long it's been since you touched their computer and when they see an error, knows no bounds.
So my policy is, I don't help people with their computers, unless their computer's are broken (won't start). Or I am willing to do something with their computer only after they agree that if something goes wrong, don't look at me.