There are three ways you can posts scripts, these are:
Inline code
Attachments
Download system
Each has different advantages and disadvantages. In general you should use:
Inline code - for short code snippets
Attachments - for more complicated code larger than a page.
Downloads system - for projects or complex libraries
Inline Code
Best for entering short snippets of code
Easiest for other users to see
May be accidentally modified by forum upgrades or when re-editing your post - it's happened before...
Inline code is entered using the "Add Code" button in the toolbar and after posting appears with syntax highlighting like this:
; This is some AutoIt code
MsgBox(4096, "Message", "Hello there!")
Code over around 50 lines will appear in a scrollable box. At this point it becomes more difficult for other users to work with and you should consider an attachment instead.
Attachments
Best for long pieces of code, entire programs, or multiple files
Unlikely to be accidentally lost or modified by forum upgrades or when re-editing your post
Counts against your global attachment allocation
Can be seen in the "username / My Attachments" part of your profile, along with the number of downloads
Multiple attachments can be added to a post. As attachments are stored as complete files in the filesystem, they are more robust than inline code snippets.
Downloads System
Best for very long and complicated projects or libraries that are of significant use to the community
Uses a different part of the forum that is optimised for file downloads and features screenshots, change logs, download counts, etc.
Does not count against your global attachment allocation
This can be accessed here: Downloads System.