Assuming you wanted to mount a share named 'Devel' on a Windows box named 'denali', like cifs://denali/Devel. You would first test this via Cmd-K and then

1. open NetInfo Manager, which lives in Application/Utilities
2. click the lock to be able to make changes
3. click on mounts
4. click on New in the Toolbar
5. click on the entry in the lower frame and start adding row, by clicking New again
6. Create the following name value pairs:
   1. name - denali:/Devel
   2. vfstype - url
   3. dir - /Network/devel
   4. opts - url==smb://<your_username>:<your-password>@denali/DEVEL

An alternative way to mount a share-point for the faint of heart, those who don't want to get into NetInfo Manager, would be to:

1. Simply mount the volume using Cmd-K and save the username and password you use in your keychain.
2. Open System Preferences -> Accounts.
3. Select Login Items tab and drag the volume into the dialog window.
4. Now the volume mounts on login, when you have network connectivity (you get an error otherwise).