you can download the SVN/GIT versions by looking here.http://sitracker.org/wiki/DevelopmentHowTo
the GIT branch is the v4.00 development and SVN is the 3.6x LTS version.
there is no release date on the v4 versions yet, but 3.66 is almost done, it needs some testing, so if you want to test it you are more than welcome.
if you are using windows, the best program for SVN is to use tortoisesvn, I don't know any gui's of git for windows, but I think there are tutorials on gitorious.org.
a quick guide, that might be alittle off, as I don't remember the menu entries, but it should be selfexplanory
rightclick and empty folder --> tortoise --> add site --> add the url in the address field
I don't remember if it makes a checkout right away, but else you can just rightclick the folder and click checkout.