Selecting "Commands | Bundle Development | Install Bundle" didn't show any option to enable jQuery in the resulting dialogue box.
Here is how I fixed the problem:
I went to https://github.com/aptana/javascript-jquery.ruble/releases and downloaded the most recent release ending in .studio3 (ignoring the ones that ended in .titanium, of course since I'm using Aptana Studio and not Appcelerator's Titanium). Just below the name of the release are several options to get the file in different formats -- I chose the .zip format.
I unzipped the file I downloaded and copied the extracted folder ("javascript-jquery.ruble-3.4.2.201308081805-studio3" in my case) into the "~/Documents/Aptana Rubles" folder. (on a Windows Vista or 7 or 8 or 8.1 machine, I'd imagine it'd be in "X:\Users\UserName\Documents\Aptana Rubles" where X is the drive on which you store your user-profile stuff, and "UserName" is the name you use to login to the computer. On a Windows XP machine it'd probably be "C:\Documents and Settings\UserName\Documents\Aptana Rubles")
After copying the folder to that location, I clicked on "Commands | Bundle Development | Update User Bundles". Gave it a minute to process that, then I clicked on "Commands | Bundle Development | Install Bundle" and the jQuery option appeared at the bottom of the list. I clicked on it, and it installed the bundle properly.
All of the projects in my Aptana workspace were closed when I installed this bundle, so I opened one up and opened its index.html file to test this new bundle. Inside a pair of <script> tags, I typed $. and immediately got code-hints. So it appears to work.
Hope this helps.
$.
orjQuery.
. In fact, type something like$.("*").
orjQuery.("*").
and you will see it available. – Everard