Many of the onboard devices will not be recoginzed before the chipset driver is installed.

Not all 8300's use INTEL NIC, Some Have 3com 3c905 chipset based nic.

http://downloadmirror.intel.com/8178/eng/infinst_enu.exe

http://support.dell.com/support/downloads/driverslist.aspx?c=us&l=en&s=gen&ServiceTag=&SystemID=DIM_PNT_P4_8300&os=WW1&osl=en&catid=&impid=

This is the INTEL NIC

That intel NIC driver worked perfectly for me - we have a Dell Dimension 8300 at home, and have been looking for ages to find the right NIC driver!