But honestly, I personally think almost all of them are flawed (no offense, that's why I'm explaining instead of just spouting out that you are wrong).
There is NO compatibility issue with an AMD or Intel CPU anymore, nor has there been for a number of years. Software companies state Intel becuase the system used was invented by them, it is called x86, and AMD is fully compliant with that. In fact, when I was a freshman at college in 2001, we had to use a program called Matlab. Worked fine on AMD machines, but actually had an issue with Pentium 4 processors for some reason, and required a patch from the manufacturer.
All DVD burners (for a PC) will also burn CDs. They tend to be higher quality than traditional CD only burners, and right now are no more expensive than a good CD burner is.
Creative makes decent products, yes. But, unless you severely screwed up a setting somewhere, almost all, if not all, modern sound cards will put stereo out to headphones if they are stereo headphones, that is why at the end of the connector, there are 3 metal portions, a common ground, and a channel for each ear.
nVidia also makes good products, I personally prefer ATI, but I have also used nVidia. Like all of the other things, I wasn't trying to say you had a bad choice, I just wanted you to be aware that there are alternatives, and your reasoning for picking one over the other may not be valid (technologically speaking of course).
Memory would be tough to do 1.5GB, it is definitely possible, but you would also be losing the current advantage of dual channel RAM which requires matched sets. Tossing in a 1GB stick and a 512MB stick will work fine, but you run in single channel.
I know that some Dell machines ship with a seperate CD, that is not the problem. The problem comes from the CD Key you were given to the machine, it is almost definitely tied to the machine, and will tell you it is invalid if you try and install it on a different PC. I tried this over New Years with a Compaq key, and prior to that with 2 different IBM keys, neither would work in a different computer. And Vista is available right now. Most places are recommending buying a copy of XP now from a place that issues a Vista coupon for a free upgrade when you want it. That way, you pay the cheap XP price, you can wait until SP1 for Vista for the securtiy issues to be taken care of before installing that. Or just jump right in, your call of course. Beware however, if you do the upgrade route, a 32 bit XP will only upgrade to a 32 bit Vista, if you want 64 bit, you need to either buy again, do it from the get go, or brave the terror that is XP64 with it's half baked drivers. http://www.newegg.com/Product/Product.asp?Item=N82E16832116200
Onboard wired ethernet makes no difference in that. If you have a plug in card, and get a surge through the ethernet, it can still take out the motherboard with it (I've had it happen). If you get a surge with onboard ethernet, there is a chance it will just fry the ethernet portion and you can go plugin route there. Either can happen in either situation. And either can also do what you are worried about, there is an option to power on a machine when it receives a signal via the ethernet port, so onboard or add on does not make a difference in safety.
That said, it is still your machine, I'll see what I can toss together for a recommended component list for you that should make you happy. In the meantime, there are worse things you could be doing than browsing PC forums and sites like the ones at overclockers.com arstechnica.com anandtech.com hardocp.com. There will be some good articles on all of them that would help put your mind at ease with compatibility and quality issues.