No problem. You'll need to download the latest version of FreeDOS for UBCD...
Once downloaded, unzip the file. Rename the image "dosubcd.igz" to "dosubcd.img.gz" (you should now be able to open the archived image using Gzip or Winzip).
There should be a file within the archive containing a *.img suffix. Use WinImage (google it) to open the disk image.
Search for the directory...
This is where you'll need to place (drag and drop) your network driver (see the link I provided with which to download the correct driver for your NIC). Once done, save the image and rename it to "dosubcd.igz" (I'm skipping the compression step for now).
Using ISO software (Nero, WinISO, MagicISO etc), insert the newly created disk image into your UBCD ISO...
Burn the ISO (or test it using a virtual machine such as Virtual PC or VMWare). Once booted, select the following from the CD menu...
DOS/Linux boot disks -> Dos boot disk -> FreeDOS bootdisk 3.40
Once loaded, exit to the command prompt and type "msnet" to begin.