ok soo I'll help you out here
for a computer
importance is usually from this list
cpu... ex intel core duo, core quad, celeron, amd athalon
i choose intel over amd because its easier to use and uses less processes.
also the more gb it can handle at once the easier programs will work.
possibly go for a duo
next its ram
more ram = being able to do more; i suggest at least 3gb if you have a new machine coming with vista, 2gb if with xp
then is hard drive space,
well now a days more is better; usually standard about 500gb and you should be set i mean what else do you do with space unless your me and download the entire internet Xd
i guess next on the line is dvd/cd drives... if you want to burn stuff make sure that they add a dvd/rw+- if you need to do burning;p most do come with at least one drive.
next is graphics cards...
the newer the card is the more it usually can do...
there is memory differences for graphics cards as well.
playing games for nowadays usually a graphics card with 512 memory is suffient.
umm and the recertifed is that they made sure everything works, just its was opened so the labor and parts usually becomes 90 days. After that your on your own
but i hope this helps