Lee, its the same as putting MP3's on a cd, you can fit (for arguments sake) 100, but if you want them in a format that a normal audio cd player can understand (cda) you can only fit (arguments sake) 15. Your best bet is to burn the episodes onto a dvd in the same format theyre in, you wont be able to watch them on a household dvd player but you can allways view them from your pc again or load them back onto it. If you burned all 5 series, 4 per disc it would probably cost more in dvd's than it would to buy the box sets.