Firstly, those versions are all very very old. jQuery is currently up to version 1.7.2! (You can quite often use the latest version even when plugins come with an older version. You'll have to test of course.)
However, regardless of what versions you have, you should only ever include 1 version of the jQuery library. Something that is likely happening here is something like this:
- jQuery 1.2.6 included
- Autocomplete script
- jQuery 1.3.2 included
- jQuery UI 1.5.3 included
- Content slider script included
When your scripts are included in this order, everything is fine up until the point where the second jQuery library is included. It will essentially overwrite the $ and jQuery variables, meaning that any plugins that have attached themselves to the jQuery object will be removed.
The solution is simple, just include 1 version of the jQuery library before all other scripts that require jQuery.
Did this fix it? If not, it might be worth putting up a sample page to see what's happening in greater detail.