It did not pass the requirements because of the Onboard Video, It seems that the Video is to low and says it cannot be install on this computer. SO I just remove the hard drive and put in into my eMachine and installed from there, Then put the hard drive back into the Dell...Works now.. There is no Aero, but who cares... Just have to use Windows XP drivers in Compatible mode.
I have installed windows 7 directly to Dimension 2400s before, in fact I am running Windows 7 Pro on an older Dimension B110. All you had to do was go into the BIOS and make the video buffer option set to 8MB instead of 1MB.