If this is a Pentium 4 machine, I suggest the OP go to Intel's download site, where an online chipset identification utility is available. Most Dell P4 machines use Intel chipsets and Windows 7 drivers are available for most of the components apart from the old "Intel Extreme" onboard video.
I have an old Dimension 2350 configured with Windows 7, and all the drivers were available save for the onboard video. (I used an 8400GS discrete video card instead.)