Either
Right-click on the file, choose "Add to archive...", and in the bottom-right corner you have the option "Split to volumes, bytes". You specify the size of the files you want... and that's it.
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Or with Winrar
Right click the video file, choose 'Add to Archive'
A dialogue box appears, bottom left there's a 'Split to volumes' drop-down menu, choose which you want
Your options are these, which are based on the different formats (Floppy Disk/Zip Disk/CD-R/DVD-R)
3.5" = 15mb (?) per volume
Zip100 = 100mb per volume
CD700 = 700mb per volume
DVD+R = 4.4gb per volume
Choose which one you want and click OK
Hope that helps.