Well, attacking people is pretty simple if you have their IP, its just like in Lisa's tutorials if you did them, ie. gaining entry to the truelight servers. But as arthur said, you really dont want to go up against most players on here, especially if you are just coming out of newbie protection, as most people on here are in groups, large or small, there are details of such groups somewhere in these forums and on the SGP forums.
It is easy enough to find IP's, you can buy them from the software page, click on 'Purchase Target IP', or look through the logs in any servers you have access to. Cracking them is simple enough, just connect to the IP with your firewall bypass and password break running, and then hit 'crack admin'. Obviously the version of your files will have an impact, the higher your bypass/breaker, the higher protects you can crack. You can find a couple of tutorials here on the forums, or you can visit the SGP forums
here for another good one for beginners.
Your first priority should be getting a good income and upgrading/researching your software, but above all, having fun! This is a game after all.
