I was in the same position as you a few months ago. I had an idea for YComb!, and I didn't know any technical guys well enough to be a technical co-founder, so I decided I was going to be the technical co-founder.
Do the SAMS guide first, then O'Reilly. Do the examples, do the examples, do the examples. That's the most important part. Even if you only have a few spare hours per day, you can get through 3-4 chapters of HTML/CSS, but I would recommend only doing one chapter of the O'Reilly book a day, since it's a bit more to learn than the SAMS book. So, it should take you about 3 weeks to work through both of those, and have at least a competent grasp on web dev. From there you can probably make your own decisions about where you want to go from there.
I would recommend picking up SAMS Teach Yourself HTML and CSS in 24 Hours: http://www.amazon.com/Sams-Teach-Yourself-Hours-Coverage/dp/... and O'Reilly's Learning PHP, MySQL, and Javascript: http://www.amazon.com/Learning-MySQL-JavaScript-Step---Step/...
Do the SAMS guide first, then O'Reilly. Do the examples, do the examples, do the examples. That's the most important part. Even if you only have a few spare hours per day, you can get through 3-4 chapters of HTML/CSS, but I would recommend only doing one chapter of the O'Reilly book a day, since it's a bit more to learn than the SAMS book. So, it should take you about 3 weeks to work through both of those, and have at least a competent grasp on web dev. From there you can probably make your own decisions about where you want to go from there.