Assumption:
First, are the any requirements for the trademark applicant to survey established names?
If the trademark is granted registeration, how can this affect other unregistered software trademarks?
Trademarks are established by business activity. There is no requirement to register a trademark.
From Business Law, Fifth Edition by Miller & Hollowell:
The owner of a trademark need not register it to obtain protection from the tort of trademark infringement, but registration does furnish proof of the date of inception of its use.
It sounds like the "proof of the date of inception of its use" can be challenged by the existing holder of an unregistered trademark.
According to the USPTO, the registrant does not appear to have the duty of searching for prior use of an unregistered trademark. See http://www.uspto.gov/teas/eTEASpageA.htm
The accepted answer here is close, but not necessarily correct.
First of all, a common law trademark (not a Federal one) is established by use in commerce, not just business activity. The best example of this is a sale, but courts have accepted less.
Yes, there are requirements for a federal trademark applicant to search for names, but only in the principle register (a list of federal trademarks). There is no duty to search for an unregistered trademark, although if they did chose this mark out of bad faith it could have been brought up during the registration process.
If the trademark becomes registered, that registered trademark will be known as the "senior user" in commerce. This means that the registrant can expand use of the trademark in the entire United States, where as the junior user is limited geographically. A registered trademark also has the presumption of distinctiveness which is important in many proceedings.