Which HDD is good for my system either existing 80GB IDE or new 160GB SATA?

I am using a Lenovo desktop computer.The system configuration is:IP4 HT 3.20GHz,80GB IDE HDD(7200RPM),1GB RAM(400MHz),16X DVD R/W and recently added a XFX Nvidia 6200 256MB DDR2 graphics card in the AGP 8X slot(disabled the onboard video),250W MAX PSU.The system motherboard supports both IDE HDD and SATA HDD.I have a new 160GB SATA(7200 RPM)HDD.Shall I remove the existing HDD and install the new HDD? or Shall I use both HDD?Please suggest.Thanks!