Not that easy
In order to hijack a range of IP addresses, you have to subvert a core ISP, or find some way of injecting false BGP (or whatever they use nowadays) information into the wider network. You have to be trusted, and in particular points in the network to have BGP info believed by your neighbours.
While I am not saying this is impossible, it is so fundamental in the operation of the Internet as a whole that if this is compromised, the operation of the whole Internet is at risk.
To El. Reg. To see whether an IP address is where you think it is, you can try to use traceroute (oh, sorry, tracert for windows users) to see where the packets appear to go. While it is not a sure-fire thing (traceroute can be blocked easily, and some routers do not respond), you may get sufficient clues from the names of the routers that have DNS entries to guess at the routing of the packets. If this does not work, you might try a ping -R (UNIX/Linux only?) to get the return path of the packets.
There are probably many better tools, but Dig (although I still use nslookup), traceroute, ping, netcat, telnet, nmap, wireshark and other tools such as nessus should all be in the metaphorical toolbox of people who want to diagnose network problems.