In TeXworks, there is a shortcut key for the current typesetting menu, Ctrl+T.
I was wondering if I could assign another shortcut key for another typesetting command.
For example, Ctrl+T for pdflatex, and Ctrl+1 for bibtex, etc.
This isn't the typesetting menu works: choosing BiBTeX from the menu doesn't run bibtex but instead associates CTRL-T to the bibtex command. So even if you could associate a key to the BibTeX menu item, it wouldn't do what you want.
There is no way to reassign keys within TeXWorks itself; It also doesn't appear to be possible to assign keys through other OS-dependent methods. For example, on a Mac, you can assign keyboard shortcuts to any menu item in any application using the System Preferences -> Keyboard panel, but this doesn't seem to work with TeXWorks. Whether such methods work in other OSes (Windows or Linux) I can't confirm.
There are some pataches here which might work for you: http://code.google.com/p/texworks/issues/detail?id=17