If you buy an IDE/ATA hard drive you should be able to install it without a problem. There are some computers that don't have IDE in lieu of SATA, but these are all brand new boxes, if your computer is a year old or more, you'll have IDE.
You don't have to solder in anything, but they're correct when they say you have to get the right kind of RAM. Check over at www.crucial.com
to match up your brand of computer or motherboard to the type of RAM you need.
To make a 1:1 copy of your original hard drive you need cloning/imaging software of some kind, like Norton Ghost or Acronis True Image.