I was comparing systems with the same processors, hard drive sizes and speeds, and everything else...
where are you getting your prices or what are you adding?
It doesn't appear that you are. Here are the differences (your config in italics):
Dimension E520 Intel® Core™2 Duo Processor E4300 (1.8GHz, 800 FSB)
The iMac has a 2.16 gHz Core 2 Duo. I priced the Dell with the 2.13 gHz C2D processor.
Operating System Genuine Windows Vista™ Home Premium
Vista Ultimate is a more fair comparison, thus included in my config.
Monitor 19 inch E197FP Analog Flat Panel
The iMac comes with 20 inch widescreen DVI display, thus included in my config.
Network Interface Integrated 10/100 Ethernet
The iMac comes with gigabit ethernet, 802.11n (112 mbits/sec) and bluetooth. Neither your or my Dell config had any of these standard Mac features as an option, as far as I can tell.
Sound Cards Integrated 7.1 Channel Audio
The iMac comes with digital optical (as well as analog) audio I/O. There's no info on the Soundblaster card, thus I assume it is a 7.1 analog signal and not digital optical. Since the iMac's is digitial optical, it can send any of the available audio formats (e.g, DTS, Dolby Digital, Pro Logic II, etc.; and probably some that have yet to be invented) in a single TOSLINK optical cable. I have one of my Minis running my home theater system and it is connected to an Onkyo Dolby Digital receiver by one of these cables.
Yes, I could have parted out a PC (and I also have done so for a home built PC w/ Win XP
). 
