Transfer - assuming old PC is XP, you'll need to download the Windoze easy transfer software to that one. Run it and save everything you want to an external HDD. Run easy transfer on new W7 PC - job done (I did just that a few weeks ago, and it was straightforward).
Choice is huge, but most new PCs have 4Gb RAM which is ample for what you want. Half a terrabyte HDD is not unusual. You will find the speed of any of the new machines much better than a clogged-up XP. Office 2010 is disliked by many who are used to 2003. Option is Open Office (free compared with a ludicrous amount for the Windows version). All the programmes are compatible.