Since as the error message says CIFS URLs (starting with smb://) are not supported, you have to use the "classic" syntax to identify the server and share. Furthermore, you cannot mount a folder within a share as though it is a share--you should mount the share and then access the folder within it. You can make a symbolic link to the folder inside the share, if necessary. Finally, when you run smbmount, mount -t smbfs, or similar remote mount commands as root (for example, with sudo), you need to specify the username on the server (unless it's actually root, which is unlikely and, if the server runs a Unix-like system, not recommended).

So first, you'll create a folder (mount point) for the share:

sudo mkdir /mnt/projects

(This is assuming you want to create it in /mnt. It's become more common to create all globally accessible mount points that aren't part of your Ubuntu system itself in /media instead of /mnt but it's fine to use /mnt if you like.)

Then use a command like this to mount the share:

sudo smbmount //192.168.2.28/projects /mnt/projects -o user=USERNAME

Replace USERNAME with the username on the Samba server that you need to log in as. You'll be prompted for your password. You can specify your password on the command-line too (with -o password=PASSWORD) but it will appear in cleartext in the Terminal and will go into your command history, so you probably don't want to do that.

You'll notice that I've used smbmount but mount -t smbfs or mount -t cifs (or mount.cifs) should work just as well, if you prefer.

Now smb://192.168.2.28/projects's contents are accessible in /mnt/projects. If you need to be able to access the contents of smb://192.168.2.28/projects/myProject in /mnt/projects/myProject, you can create a symbolic link:

sudo ln -s /mnt/projects/myProject /mnt/myProject

For readers of Ubuntu 12.10 and later: You must use mount.cifs or mount -t cifs (smbmount and mount -t smbfs are no longer provided). The cifs-utils package is required. These commands will work on earlier systems too.