http://www.west-wind.com:8080/svn/WestwindWebToolkit/trunk/
Please be aware that code between releases may be in flux, but it's a great way for you to receive fixes and updates to issues you might have reported that have been addressed between releases.
For patches the more granular the better is usually the key, so try as much as possible to isolate any changes you make.
http://www.west-wind.com/presentations/subversion/
TortoiseSVN
If you just want to download and keep in sync with the repository the easiest and free way is to use TortoiseSVN which is an Explorer shell extension that allows creating, accessing and updating of repository data easily and visually through Explorer (or Explorer replacement).
To download the Web Toolkit with TortoiseSVN simply choose Checkout, point at the repository path above, and choose a target directory on your local machine, and it will retrieve the entire project for you.
http://tortoisesvn.tigris.org/
VisualSVN for Visual Studio
VisualSVN offers a nice clean and non-SCC based add-in for Visual Studio that leverages TortoiseSVN inside of Visual Studio. You get a similar UI as Tortoise SVN and the smarts that knows about Visual Studio specific files that should be ignored or handled as a group (ie. adding an ASPX file will add the related source and designer files as well). VisualSVN is not free, but in our book totally worth the small registration fee.
http://www.visualsvn.com/
AnkhSVN
Ankh is another Visual Studio add-in that was idle for some time but has seem more development recently. Ankh uses the Visual Studio SCC provider to integrate with Visual Studio.
http://ankhsvn.open.collab.net/
Both tools work well and simplify the process of dealing with Visual Studio specific projects inside of the Visual Studio shell.