The "ratings bar" for each kit or project provides a relative measure of how complex the installation process is.
Beginner level projects (green) generally require no soldering but usually involve removing socketed chips and plugging in replacement boards. Beginner projects will usually not require much more than common hand tools and a willingness to follow directions.
Intermediate level projects (yellow-orange) will likely involve some soldering and small board-level modifications or running a few wires in addition to the Beginner level activities. Intermediate projects will usually require an average quality low-wattage soldering iron and tools like wire-strippers, clippers, etc.
Advanced level projects (red) will typically involve soldering and understanding of diagrams and electronics concepts. The kit may require user-supplied components or it may be used as a "building block" for a more complex project by the user. Advanced projects may require electronic test equipment, device programmers, etc.

All projects require a basic understanding of safe handling practices for electronic components and static-safety in addition to basic socketed chip removal techniques. These are covered to varying degrees in the manuals, but please ask questions or recruit help from a more experienced person if you're uncertain of a procedure or practice!

2001, Clayton Cowgill