You need to "mount" the server share - once you've done that, you'll be able to access it as though it were a local directory (this is more-or-less the *nix equivalent of mapping a network drive to a drive letter). To mount Windows shares, the CD uses Samba
There is a directory named /mnt which is traditionally used as a base for mounting network shares. System Rescue CD has had a bug in the past (don't know if it's fixed now) that meant you shouldn't mount things directly in /mnt, but in a sub-directory.
Create the directory where you will mount your Windows share. Open a terminal and type:
Then, to mount the share, type something like:
or (if you don't need user/password):
mount -t smbfs -o "lfs,username=WindowsUser,password=WindowsPassword" //126.96.36.199/share/ /mnt/win/
The "lfs" option enables large file support, which is needed to handle files larger than 2GB.
mount -t smbfs -o lfs //188.8.131.52/share/ /mnt/win/
Once that is done, you can simply run partimage and set the image file to something like