If your buying a new mac to replace an old one and you have time machine, make a backup, then, when you get your new mac you will be able to set the new computer up very easily if you have iWork that will transfer over as its not tied to a particular computer, unlike Quark Xpress, iStudio Publisher etc if you have any software that is locked to your old computer then you will have to de-authorise it, iTunes should be de-authorised too before hand.
If you do not hand time machine, but can get a copying software, such as Carbon Copy Cloner, you can copy your hard-drive and use that to set up your new Mac.
ps. If you bought iWork as a download you should be able to copy it to a cd/DVD
Cheers, Macjim.