Since you're not going to find a machine that is exactly the same form factor as the iMac, and you've already gone to a separate cpu, you might as well just get the Dell 3000 2.8 ghz P4 which is $379 (after $100 rebate) and choose the 17" flat panel add on, which right now is $270. Now you start out $559 lower than your original Dell machine/monitor combo, and have 512 mb memory to boot. Your total Dell price is now $1058, or $441 cheaper than the iMac, even after you add on all the extras.
[url=http://www1.us.dell.com/content/products/features.aspx/outrageous_desktops?c=us&cs=04&l=en&s=bsd]http://www1.us.dell.com/content/products/features.aspx/outrageous_desktops?c=us&cs=04&l=en&s=bsd[/url]
I love my Macs, but PC's still have the market on getting powerful, flexible, inexpensive gear into the hands of consumers. Sure, if you just walk into the front page of Dell and order whatever is there, you might end up with a full price machine, but Dell (and everyone else) offers too many deals and specials to ever buy a stock retail price machine.
Thing is, iMac still is targeting the home user. Most home users I know want to upgrade their machines, and already have a monitor..and in many cases a flat panel. It's pretty hard to convince them to pay $1000 for any kind of mac (more like $1200-1500) that doesn't have a monitor attached, when they can get something pretty decent out of the box for $379.
New iMac is $118 Cheaper Than A Dell