Where are you getting these newer drivers from?
The Dell support page for your Dimension 4700 lists drivers
http://www.dell.com/support/home/us/en/04/product-support/product/dimension-4700/driversthe audio is from 2005, chipset 2004, modem 2004, 2005 and 2006 depending on the hardware inside your tower, video 2005 and 2006 again depends on the hardware.
I would not recommend downloading drivers from any 3rd party sites.
The newer drivers that you think you need might be to add function for Vista, 7 and 8 but won't do a thing for XP.
As I mentioned previously, I rarely update drivers. We have a Dimension 2400 (also from 2004, same as the Dimension 4700) running XP and an Optiplex 745 (2006) purchased refurbed and upgraded to Win 7. I haven't touched the drivers in either computer.
Phones use 3.5mm audio connections, not USB, the same as a computer's audio port.