I was playing with PHP and ASP.NET in the last days. In fact, Visual Web Developer 2010 Express is a great IDE. However, sometimes you feel that you are not a real programmer. Depending on dragging and dropping make you out of real programming box. Although you can switch to mark up (source) and type ASP.NET markup, but I hated the server controls and the run at="server". As they make the development quite easy in some aspects, they made some simple things quite complicated as well which make you feel confused and the time you spend in organising yourself inside this environment will make the PHP programmer cut the half way of reaching his goal.
With PHP you can feel the flexibility in controling your code. The sad point about PHP is the bad reputation of security and as I saw in many threads some say this is according to the bad practice of newbies. In some countries most universities websites and government websites have moved to ASP.NET not because of the fact that it is more secure (as some say) but I think because of the bad reputation of PHP out there.
To conclude, I would say that PHP was a good choice of start for me and I see that the security issue in PHP will make you learn about security beside PHP and leave you learn more than others so you can look at your code and developement from different perspectives. I think this is the longest thread I have written in sitepoint forum and I hope you share your ideas!