Vista's a decent OS. Memory seems to be the biggest component to getting it to run well, so 4Gb should be fine. I'm running it on laptops with only 2Gb on my work and home laptops without many problems.
Most annoying thing you're gonna face when you first get it is the User Account Control (UAC). This is the thing thing that pops up to ask you if you're sure that you actually want to perform the action that you're trying to perform. You'll probably want to
disable it within your first 5 minutes of use.
The biggest thing to get used to, IMO, is that the directory structure is a bit different. They moved some stuff around so it takes a while to get the feel of where some things are located. It's also required me to edit some installation scripts that I use which copy files to areas and delete some files as well.