A good friend of mine wrote this awhile back, with the intention of trying to market the underlying code. He's been too busy to get very far with it, but the product is out there. You can download a trial, and it will do most of what you want. It does a network discovery, pingsweep with SNMP requests and everything, dns reverses, etc. Probably has a lot more than you want, but it should work. Windows only, I believe.

http://www.dbapsoftware.com/