* Installation refers to the process of installing something or the thing that is installed, often in a larger system or project. Examples:
* "The installation of the new software was a smooth process."
* "The art gallery has a new installation of contemporary sculptures."
* Installment refers to a part of something that is paid or delivered in stages, often in relation to a loan or a series. Examples:
* "She made monthly installments on her new car."
* "The novel is published in installments, with a new chapter released every week."
So, the best noun to use depends on the specific meaning you want to convey.