You haven’t stated your version of Photoshop. If it’s "CS", then the following may NOT apply, I don’t know.
Basically, you create an action to Save As JPG. Then you run File|Automate|Batch on a folder of files, using that action.
Basic overview.
Open a dummy image, start recording, File|Save As. Carry the steps all the way through actually saving the file, then stop recording.
Toggle the dialog of the action to OFF in the actions pallet (the little square next to the action name).
You are now ready to batch.
File|Automate|Batch
Action to run = the one you just created
Source = Folder
Choose = select the folder containing your tiffs
Destination = Folder
Choose = select where you want them to go
Override Action Save As Commands = CHECKED
Optionally choose a naming convention and hit "GO". Each image in the source folder will open, then Save As JPG to the selected destination folder, then close.
Peace,
Tony