Nope, probably not GoogleBot. They use valid IP addresess. 0.0.0.0 is not a real IP address. My guess it was probably something invalid being returned by a proxy, or your hosting server is having a problem. Is it a Windows based server by chance?
Yeah no bot can have that ip adress, no one can it 99% likely to be a software malfunction or hosting error. I have seen windows do it before but it can also be a broken script if you are using java to track it.
I really don't know much about this, but sounds like a common header spoofing. Some forums use the X-Forwarded-For header to get the IP address of a visitor. This header can be easily spoofed to just about anything using Proxomitron or similar MIM proxies. 1.3.3.7 is a common one for some odd reason..
It's a way people can evade bans on their IP. I know phpBB 2.0.6 and below are vulnerable to this. You can probably find a patch to fix your version to make sure you're getting the correct IP address.
Problem is there is no safe way for the developer to be have a correct direct IP to the user browsing. A few years back you would rather often ban entire ISPs using the same proxy by banning the IP making the request. In those times the forwarded header was a much more practical way of banning 1 user instead of 1000. Now on the other hand, most ISPs have grown aware of the foolishness of such proxy solutions and banning the IP making the request is becoming rather safe. You still face the same problems with users in some schools and coorporate buildings though.
That would be because it's 1337 / leet / some "hacker" trying to act cool.
Anyways, most forums will identify bots for you, so you won't have to look at the IP. Unless you have members banned by IP, I don't think this is anything to worry about.