For the ram and hard drive upgrade no you don't need a new PSU, for what it's worth Dell's PSU's are decent units that will power the PC in stock form for many years there just isn't a lot of head room for high power up grades(video cards) and numerous external usb devices.
Acronis True Image is one of the better image programs, WD has a program called Data Life guard of Dos the will copy your existing drive to the new one>
http://support.wdc.com/product/downl...sid=53&lang=en