Please help with Dimension 4600 upgrade

Hello,

I have a 2003 Dimension 4600 APG.  With a seagate 80GB HD.  I was hoping someone would help choose the right HD for my computer.  I've upgraded the RAM to 4GB.  Now I want to throw in a fast harddrive.  Dell parts upgrade is recommending WD HD 750GB 32MB cach @ 7200RPM cavair black.  But this is a SATA drive I believe my seagate is not it is hooked up with a IDE ribbon.  The 80GB has a SATA port but is not hooked up that way.  I do not have any SATA cables.  I worried that if I use another IDE drive that it wont improve performance.  Also I would like to keep the Seagate and perhaps set it up as a slave.   I dont know I really dont much about doing this.

Please help,

Thank you

Roger