Server Software

Hey All, i recently lost my server due to a bad apple in my client list, they sent spam, violated my tos, and my servers tos and they used a proxy and gave false details, so i lost my server...

I am looking to set-up again, but this time using dedicated servers of my own.

Is there any software, free if possible that can monitor a server for spam, of search scripts on a server for phpmail extensions, etc?

I am also in need of other software, i am not sure if i should go windows or linux, i need at a must PHP, ASP, and AJAX and a free control pannel.

Any ideas?

I have got a server already, its loaded with CentOS and thats it right now, i got a great deal as they dont install any web extensions, etc. I also have full access so i can change it to Windows or another Linux type if needed.

Thanks for any help...