another thing to consider is buying and building it on its own is that every part will usually come with a much better warranty that the prebuilt packages at Dell, Gateway, etc.
When I bought a Dell a few years back it came with a parts warranty. I had to replace the modem, video card, hard drive, and the motherboard... twice. When I build my last system, I had a four year old hard drive fail on that system and that's it. Now your mileage may very, but IMHO if you buy quality parts the warranty doesn't mean as much.
Lets see..
I build custom gaming machines as a living.. sets check warranty product information based on off the shelf vs build your own.
Dell, standard 2 year warranty (unless you pay the extra $250 for an additional year)
Same for HP, Compaq, Sony, Toshiba, Etc..
2 Years is the standard warranty for the entire computer, which includes all internal parts.
Custom build system
Case, Lifetime Warranty
1000 watt power supply, Lifetime Warranty
2 NVidia Video Cards in SLI, Lifetime Warranty
gigabyte Motherboard, 5 year warranty
intel CPU, 3 Year Warranty
Hauppage TV Tuner card, 2 year warranty
Patriot Extreme RAM, Lifetime Warrany
Asus PCIE x4 Ethernet Card, Lifetime Warranty
3 1/2 Floppy Drive, 3 year warranty
DVD Burner internal, 5 year warranty
DVD Burner External, 10 Year warranty
Western Digital 3gb/s HDD x2 in Raid 0 Striped (1 TB total space), 3 years warranty each drive.
Now the only component that has the same warranty that a pre-built machine has is my TV Tuner card.. the rest of the system exceeds the standard warranty.. and half my system is lifetime warranty.
So what you stated about your pre-built system warranty vs a custom built system warranty holds absolutely no water what so ever.
Now going apples to apples on a decent machine.. Go to the Dell site and find a system that you like.. and I will price out the parts in a custom system that will either meet or exceed the Dell system with a much better warranty option and costing less than what Dell is offering by at least 20%.
Just pick out a system within you current price range.. and with the difference in price, I'll even put in some options that exceed the options that Dell offers.. when I can direct you on the ordering and how to build..
it is pretty simple.. and I am only doing this once.. I am looking for business, not trying to teach others how to do my business..