Phædrus2401

That is an excellent hard drive, Western Digital is a very reliable brand and that is a good model, though unless you're saving a lot of music and movies to your computer, it will take you a *long* time to fill it up. However, it requires a SATA interface and some computers over ~5 years old have only an IDE interface. Looking the computer up on Dell's website only says that it supports two 320GB hard drives (it probably has the Western Digital Caviar Black 320GB version in a standard HDD cage, so if you take it out the 1TB should fit). I don't know if your computer has IDE or SATA or both, so I can't help on compatibility.

I don't trust any product by Norton, personally. After bad experiences with Norton 360 on my brother-in-law's computer (identifying everything BUT the virus as a virus...) I've decided that Norton just isn't worth messing with. Try googling "freeware hard drive cloning program" (freeware because it's free and it's *often* made by enthusiasts who probably use the program themselves).

RAM and hard drives don't require much power, so it's unlikely you'll need a new PSU to run them. If you plan on making any other changes, I would consider one. Dell's website says you have a 305 watt PSU, and Dell PSUs are ****, so if this were my computer I'd get a decent quality 450 watt PSU (though I would never buy this computer in the first place), but if it works now it should be able to power your HDD and RAM as well.