It can be easy to install vinyl windows. First, make sure the window frame is plumb and level. Wrap the window frame with insulation, or pack the insulation into the void between the frame and the window. Center the window in the opening, making certain the reveal is uniform on all sides. Use shim singles to secure it in place and check for level once again. Finally, drive two quarter-inch stainless steel screws into all four corners. There you have it.
For more on windows, consider:
Replacement Windows 101
Installing a Vinyl Window (VIDEO)
Know Your Window Styles: 10 Popular Designs