ASP and PHP are similiar languages in terms of scope and ability...PHP is easier to learn, as it is a more mature and fully developed language, though I found ASP quicker to master as I came from a VB background...
ASP and PHP work the same way with databases, both can create SQL statements, then open a connection (PHP handles this better than ASP), runs the query and returns the result...
my advice, given that you don't have much ASP experience, is to stick with PHP. Master it, breathe it and love it...you will find it a much more rewarding experience especially now that ASP is moving to ASP.NET which is an entirely new creature using VB.NET or C# (C sharp) to create the code...
The other thing to consider is that a true ASP IDE will run about $1000 (for visual studio, which includes VB, Visual Interdev(web tool), C++, and MS Java (J++))though there are some good free or cheaper tools out there. PHP has a plethora of IDEs that are availalbe with many being free (PHP Edit amoung others)
hth