Ubuntu 10.04 RC was released yesterday and is available for download at the official Ubuntu release page. Head over to this page, navigate to the bottom and there, you will see a number of releases for you to choose from.
If you are interested in the DVD and the source CD, visit this page instead. This includes most common Ubuntu custom distros featuring different desktop environments.
Please do not put the entire load on the main servers and user the download mirrors if possible. The list of download mirrors is also available. A common system requirement is 256 MB of RAM. If you own a newer Intel processor powered Mac system, good news is that you can install Ubuntu on it as well.
This page includes the server, netbook, alternative and the very common desktop version. The desktop version is also a Live CD so you can give Ubuntu a try and decide on whether to install the final version or not. This will not alter your current installations in any way.
A great software to consider when installing Ubuntu with Windows is Wubi. If you want to try Ubuntu inside Windows, go for Windows Ubuntu Installer Wubi. It makes Ubuntu easy to install and does not make any major changes in the boot-loader.
My suggestion is that, with the final version only a few days away, you should wait for the final version though surely, give this RC a try.