There's a microcenter in California?! Where? Probably far down in the south.
It should be a big difference from onboard to dedicated, but I can't say for sure as I don't have a functional soundcard at the moment. You could always bite the bullet for one.
As for the microphone, I heard that logitech one is great.
You can also make a removable boom mic as Fragtality
with any old headset or a cheap one off some site.
Since the AD700s are open, it might very very very slightly have different sound (not necessarily bad) but you probably won't notice a difference at all.
I also saw some guys mod they're headphones to have a mic in jack on their headphones and get a $3 flexible mic on Amazon to attach to it.
You probably wouldn't go that far though.
EDIT: Fry's suck, but its the only computer store I have.
Also, Fry's isn't bad. They price match anything online. If something is cheap on Amazon or NewEgg, I just go there and they price match it for me .
Thanks for the info as well, Repped.