How Can Marketing And Techies Best Work Together?

Chris Worth asks: "Something Slashdotters could help with here. We all know that asking a hacker for 'business' stuff like accurate deadlines and costings can be next to impossible. Trouble is, you can't run a business without this stuff... forcing us marketroids to guess it. So plans are laid, budgets are forecast, and schedules set without reference to the techies. Generally, this all ends in tears. What's a reasonable way to estimate the size and cost of a 'normal' (for example, a database-driven customer service app, with no fundamentally new technology needed) Web development project? Is there some equation - perhaps linking together number of program variables, length of spec document etc. - that'd lead to a decent guess as to how long a given number of people could reasonably be expected to deliver the project in? In other words, how can I be fair to my programmers?" It's nice to see someone in marketing trying to go that extra mile to make sure their programmers have enough time to do the job, but reality being what it is, this luxury happens infrequently enough. What would you techies want from marketing and what do you folks who work in marketing want from your IT staff? Is there a way to work things out that would make most camps happy?