Is it possible for two people to have same I.P address?

A member joined my forum the other day and I decided to check their I.P address as Something didn't ring true about them going by their first post.
It came up with their I.P address but also there was a list of 4 other users posting from the same I.P address. All their profiles were obviously different from each other and the areas in which they live are no where near each other.
What are the chances of them all being the same person with different aliases?
Is it possible for more than one user to have the same i.p address? How can I check this?

Thanks for any help you can give me

Yes it is possible for multiple members to have same I.P address. Check the posts of all members, if they are spam, and they probably are because no 2 internet connections can have the same IP, than they probably think that you cannot trace them, but you can! So check them out and delete/ban if nessessary.

Hello.

This can happen :
- if these people use computers which are connected to a same network (at school for example.
- if these people are under the same ISP and have an IP which changes everyday, so the member A can have the IP X today, and and the member B can get this IP two days later.
- if these people are under a same proxy (it's the case with AOL users).

Well the I.P is coming up as the same proxy "AOL". Is that it?

Thanks for all your help everyone, much appreciated

Janey x