I've been fleshing out my IP address spreadsheets, and I've been using a trick that I didn't know about for a long time, till someone on a forum showed me. It was indispensable.
You know how, if you want a series of numbers down a row, you can click the lower right hand corner, and drag it down, and it autoincrements the numbers for you? Well, in oocalc, if you try that with IP addresses, it just copies the original IP address. I don't know why, but it does. MS Office gets it right, heck I think even K Office will do it. OpenOffice, not so much.
The trick to doing it is to put a space in front of the IP address, first.
" 192.168.0.1" will allow you to drag it down as far as you want, incrementing the last octet.