If it's a decent RFP (request for proposal), it should specifically list exactly what it is they expect from you in the tender. If it doesn't, it sounds like a poorly written RFP and hence you should think carefully before spending your valuable time on something that involves too much guesswork on your part. RFPs tend to have a low probability of success at the best of times, but without a clear list of requirements, you're really stabbing in the dark.
If it's a little vague, consider ringing the listed contact person and grill him on their requirements in more detail (this is a good idea for all RFPs anyway). Don't just stick to technical stuff, ask them questions like
'How many other developers have you approached?'
'What are the main criteria you will use to select the successful applicant? (i.e. value for money, expertise, cheapest, most experienced etc)
Who wrote the RFP (in-house, or was it a competitor? If so, chances are they are first choice for the job)
What is the budget for the project?
Answers to questions like this will tell you whether or not it's worth all the time and resources responding.