If you are doing any scripting for this, see the script in this post to make sure you hit the user and not the proxy server. Apologies if you are already aware of this issue, but wouldn't want you to ban hundreds of users instead of just one.

yes as peekay says.. be careful when issuing IP bans, as another reason they should only be a last resort is that many users have dynamic IP addresses (ie they change IP everytime they reconnect to the internet) ISP's typically are allocated a set IP range for their customers, so if you have many dial up users etc lets say they use AOL ISP to logon to the internet.. AOL has an allocated IP range, that means those users will always have an IP in that range.. so 1 user could cause problems with you, but if u ban that 1 IP address, then if you have many other users also with AOL tyou could inadvertently ban them too because the next time they connect they could be issued with that IP address even tho they aren't the original person you banned..

ok, but i'm not so interested in banning as in IP address log. So, can i make table with attributes - ID, IP, username, time. And every time someone enters my site, the data will be written to this table. How can i do that?

Anyone know of any updates since this issue was last addressed? I know there is a way to log user IPs because I used to belong to a site (created with Xoops) that started banning specific users. I tried the php-stats link and couldn't get it to work. I am having similar problems with certain users and I would also like to know how to log their IP addresses. Thanks in advance!

Thanks to carnuke
I manage to install PHP-Stats by using this small guide.
You can see it HERE

I use PHP-Stats for the same purpose.
With detailed user tracking, Its a handy tool for webmaster.