jQuery can be downloaded from the following link, is currently at version 1.3.2, some tube problems, as it used to use version 1.2.6 and some plugins did not went well in 1.3.2 as idTabs (very good) , jClock etc.
As an additional component, jQuery has a library for the generation of user interfaces, jQuery UI. Basically has the following elements (Widgets): Accordion, Datepicker, Dialog, ProgressBar, Slider, Tabs.
These widgets, along with the possibility to use effects (Blind, Bounce, Clip, Drop, Explode, Fold, Highlight, Puff, Pulsate, Scale, Shake, Size, Slide, Transfer) and interest (Drag, Drop, Resize, Select, Sort) make this a powerful tool library for developing AJAX applications.
I found one interesting job offer for freelancers who know jquery :