My Vostro PC (from Dell) is eleven years old and the hard drive is showing signs of being flakey.

Everything is backed up; it's just a matter of whether to replace the PC or the HD (320GB Serial ATA Non Raid (2x160GB) 7200RPM dual HDD Config).

I've changed HD's in previous machines - and don't want to go down the external HD route.

Any thoughts on this decision including where to shop for a new HD (I'm looking for 500GB and reliability) and compatibility of interface connection issues?