Is it possible to first enter a command and then choose "run in Terminal" in Quicksilver?
First, you'll need to install the Terminal Plugin.


Run any command from Quicksilver? Just enter text mode (by pressing .), enter your command and choose either the "Run Text Command in Terminal" action (opens a new terminal window and runs the command) or the "Run Command in Shell" action (runs the command in the background and returns the results to Quicksilver)
Run a script? Just browse to the script and choose the "Run" or "Run in Terminal [...]" actions.