I wouldn't install the beta ('Release Candidate') over your current OS. Driver support will be bad, and there's bound to be several bugs etc. It's a good idea to run it as a second operating system though. I use it in a virtual machine - much easier than actually installing it onto my PC's hard drive. This seems to be a good way of finding out how good it is, and may help you decide whether you want to buy the proper version when it is released
Agree with jezzer, would not install it over your original OS. Actually I would install it on a second HDD if you can. Driver support doesnt seem to be an issue at the moment tho. Most vista drivers work with things like sound cards etc, and Ati and Nvidia both have drivers for windows 7 out.
Ive installed it on three PCs now (two desktops and a net book) and ive only needed to download one driver and that was for the netbook's function keys.
I find the driver situation to be fantastic compared to older OS's.
Due out on 22 Oct, RTM is supposed to be first week in July.
Now using it as my main OS on my laptop, although I have Vista on a partition if needed.
As all my stuff has Vista drivers the Vista drivers work with Windows 7. Devices such as printers just downloaded from Windows Update, and my flash card reader even prompted Windows to download the driver directly from Acer.
I must say that I thought Vista was good, I never had driver issues even from launch, but MS have been really smart by essentially building Windows 7 as an addon to Vista. If your computer works fine with Vista, it should run atleast as well on RC1 as long as you don't run some obscure software and hardware.