Hello Charlot, and welcome to Seven Forums.
A custom install is almost the same as a clean install, but with your current Windows installation backed up to the
Windows.old folder during this custom installation. After the custom installation, you can copy any files you wanted back in the
C:\Windows.old folder back into your new installation of Windows 7.
Like with a clean install, you will need to install all of your
drivers and programs again after doing a custom install of Windows 7.
You could download all of your
drivers and etc... before doing the custom install, then copy them to a USB flash drive to have them handy after finishing the custom install.
Hope this helps,
Shawn