the default, and only, installation option with Snow Leopard is what used to be known as an Archive and Install.
That procedure would rename the existing system folder to Previous System Folder and put down a brand new copy from the installation DVD.
Your user folders would remain intact and be put back into the correct location at the end of the install.
Under Snow Leopard, the same thing happens except that there is no longer a Previous System Folder left behind to take up space.
Go ahead with the install, your data is safe.
Of course, it is always a very good idea to have a good backup before you start any major project.
I'm runninng the very latest Snow Leopard 10.6.4 on a 2x2.66 GHz Dual-Core Intel
I need to reinstall my OS and I need to know if I will loose all my info in the Users folders, like all my Documents, App's support stuff like that?