Install this

http://www.dell.com/support/drivers/us/en/19/DriverDetails/Product/latitude-d420?driverId=5870X&osCode=WW1&fileId=2731098284&languageCode=en&categoryId=UT

Then this

http://www.dell.com/support/drivers/us/en/19/DriverDetails/Product/latitude-d420?driverId=R0THY&osCode=WW1&fileId=2731091300&languageCode=en&categoryId=CS

Then this

http://www.dell.com/support/drivers/us/en/19/DriverDetails/Product/latitude-d420?driverId=04VK6&osCode=WW1&fileId=2731090506&languageCode=en&categoryId=NI

Then you 'll need to determine which wireless adapter you have and install the appropriate driver from here:

http://www.dell.com/support/drivers/us/en/19/product/latitude-d420

Support is ending for Windows XP which will leave it more vulnerable:

http://www.microsoft.com/en-us/windows/enterprise/endofsupport.aspx

Its recommended you upgrade this system to Windows 7 or 8.1 32 Bit:

http://dellwindowsreinstallationguide.com/

See here for drivers:

http://dellwindowsreinstallationguide.com/driver-sets/latitude-d-series-laptops/

My Windows Reinstallation Guide also instructs you in how to evaluate Windows 8.1 and 7. Its recommended to try out Windows 8.1 before purchasing a license.