As was the case with the beta, don't treat the RC as a standalone upgrade. You will save yourself the most trouble by having a dual-boot system.
That said, the RC will, like the beta, install as upgrade on a Vista install, but you should only do so for the sake of testing the feature. It won't upgrade-install over the beta. You will need to create a new installation if you have been using the beta.
Whereas the beta ends in a couple of months, the RC will continue until mid-2010, possibly even operating beyond the official retail release. This is a boon for anyone who felt that a few months was too short to really get settled and see what the OS is like when you have to depend on it.
As always, a new install is only as good as its drivers. Win 7 has a pretty good stock of drivers and you can of course use Vista drivers, but there are catches. Win 7 does not like unsigned drivers and to use them you need to disable driver signature enforcement at boot, at every boot. A lot of big name makers don't bother making the drivers that they should, like drivers for 64 bit operating systems, so it's not like you can always just get it off the website ahead of time, or if it is there, it might be a beta (an unsigned beta).
For those odd ones, what you really want is for Windows to just connect to the net and get the driver it thinks it needs. Unfortunately, if you've got a problem with your wireless network card, it might not be so simple.
Luckily, it is a little known fact that you can manually browse the Windows Update catalog. Just find the right device, download the driver to a safe place and then go ahead with your new installation. You can also get other things that Windows automatically updates. There are times, rare times, when this is an incredibly useful tool.
Microsoft Update Catalog