http://support.dell.com/support/downloads/driverslist.aspx?os=WW1&catid=3&dateid=-1&impid=-1&osl=EN&typeid=-1&formatid=-1&servicetag=&SystemID=DIM_PNT_P4_CEL_2400&hidos=WW1&hidlang=en&TabIndex=&scanSupported=True&scanConsent=False

This page should get you to the audio drivers for the dell 2400 - select the one relevant to your system