GPL - please help!!!

Hello, I'd like to know if phpADS, that is released under the GPL, can be freely used for commercial pourpose. For commercial pourpose I mean: Supposing I want to build up a company like "doubleclick.com" 1. I run the program on my servers 2. I charge not on a per banner basis (Each client doesn't pay different costs for different number banner loaded- So, a client with 100 different rotating banners pays the same as one client using just 2 rotating banners) 3. I charge for impressions. So, in theory, I charge clients for the bandwidth they use. This means I charge clients for the service they receive, and the "amount" of service they release. 4. I don't sell copies of the software. I don't do any modifications of it. Please help me. I can't understand the following part of the GPL named: GNU GENERAL PUBLIC LICENSE TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION 0. This License applies to any program or other work which contains a notice placed by the copyright holder saying it may be distributed under the terms of this General Public License. The "Program", below, refers to any such program or work, and a "work based on the Program" means either the Program or any derivative work under copyright law: that is to say, a work containing the Program or a portion of it, either verbatim or with modifications and/or translated into another language. (Hereinafter, translation is included without limitation in the term "modification".) Each licensee is addressed as "you". Activities other than copying, distribution and modification are not covered by this License; they are outside its scope. The act of running the Program is not restricted, and the output from the Program is covered only if its contents constitute a work based on the Program (independent of having been made by running the Program). Whether that is true depends on what the Program does.