It's not easy to explain the difference between ASP and ASP.NET, but the second is object oriented and all the element of the page are object.
In ASP.NET you can use the language you want to use to prodece the page (VB.NET or C#).
All the code is in a particular file that is not including in the web pages and you must recompiling when you make changes, because ASP.NET using compiling language.
The compiling of the page was made at the server the first time and in the next run reuse this compiling result.
This is a simple introduction to the differnce between this two language, but is not sufficient to define the difference of this two languages.

So would you say that i have to learn asp before i move on to asp.net?

No it is not necessary you can start directly with ASP.NET, but you must chose the language that you want to learn VB.NET or C#.
I prefer C# but for the web application probably it's most used VB.NET, the best is to study both. :cheesy:

Is there anything that either of these can do that PHP cannot, because at this rate, I think i might just stick to PHP!!!

well, it compiles for better speed. It is highly integrated with the server and OS so you can some really cool cacheing things to get speed. Easier to code in because of the .NET framework. Don't have to write every thing out from scratch leaving you time to actually focus on getting a problem done rather then type out code 100 times. (to me) has better support and community than php.

what is difference between asp and asp.net

Biggest noticeable difference: ASP (Classic ASP as it is known) is a Script Language (i.e VBScript), where as ASP.NET is a the web formulation of a Compiled Language (i.e. Visual Basic, C#, J#, C++.Net)

Read this article to find out the differences between ASP.NET and ASP.
It clearly explains the differences from programmers stand point.

Differences between ASP and ASP.NET

Hope it helps

another fun thing is that the .net IDE has a WYSIWYG feature so you can build web pages visually, then fill in the parameters. this also "writes" the basic code for your design, and you simply fill in the functions and attributes you need afterwards in the codebehind or the actual page... a very nice feature that can cut down on code time and development time. this WYSIWYG feature is also simple to use with web services also.