If you cannot use the Internet,you will need access to another computer that has a connection.
From there save mbam-setup.exe
to a flash,usb,jump drive or CD. Now transfer it to the infected machine, then install and run the program. If you cannot transfer to or install on the infected machine, try running the setup (installation) file directly from the flash drive or CD by double-clicking on mbam-setup.exe so it will install on the hard drive.
Manually Downloading Updates:
Manually download them from HERE
and just double-click on mbam-rules.exe
to install. Alternatively, you can update through MBAM's interface from a clean computer, copy the definitions (rules.ref) located in C:\Documents and Settings\All Users\Application Data\Malwarebytes\Malwarebytes' Anti-Malware from that system to a usb stick or CD and then copy it to the infected machine.