I built my PC for approximately $600-$700 after all was said and done, buying mostly off of Newegg. It offers superior power in some ways to those PCs, and slightly inferior in others (weaker video card, DDR2 RAM instead of DDR3 although I have twice as much RAM in mine). And mine totally looks more badass than either of those.
No way should you buy anything - much less those - prebuilt.
note: I can't give a precise price-point because (1) I didn't buy it all off Newegg - I got SOME stuff at the local Microcenter, and (2) I've upgraded it a couple times since I initially built it (extra high-airflow fans (this sucker runs at below 100ºF/38ºC average even when under a load - you won't find a factory-built system with remotely comparable performance that can do that), another HDD (I have 2TB total =D), and upgraded from 2.6GHz dual-core Athlon II to 3.0GHz quad-core Phenom II).
SW-5120-1900-6153
Essay Pro