Turkbear is right, Apache does have an add-on that runs asp scripts.
As far as becoming obsolete, yes (unfortunatley) it will - only because PHP came out and is free - almost everything to do with it is free from the server, add on components, databases...etc...
If you sit and forget about the method of coding and simply accomplishing the task at hand it doesn't really matter what language you use. I, however, have recently started to learn PHP because some of my clients, and almost all new potential clients, want to save money and go the PHP route.
Everything I've read to compare the two languages focuses on cost:
PHP is free to download
PHP runs on LINUX/APACHE which is free
PHP uses MYSQL which is free
If you want and FTP, Image rendering, upload script, you can get these for FREE with PHP, wheras with ASP you'll need to spend money on components. With ASP you either have to spend lots of money on a CMS or custom build one (which takes time + time is money) wheras PHP has free solutions like Joomla and Dupral (to name a couple).
The articles also focus on speed saying PHP is a lot faster. Which, I guess is true, but with the speed of servers now-a-days, I don't see speed being a big concern.
Like Greg said, The other reason classic ASP will become obsolete is because Microsoft is focusing their efforts on ASP.NET now, and more and more developers/programmers are going that route.
It really comes down to how good of a sales person you are. I do have one client still that sells classic ASP and does a pretty good job of it. He gets new jobs all the time and convinces the company to use classic ASP. This works out well for me as he in turns sends the work my way to complete.
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GOOGLE is a great resource to find answers to questions like "how do i..."
If you don't know exaclty what you want to do or what to search on, try Google Suggest:
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I have recently been semi-converted to ensuring all my code (well most of it) works in both javascript and non-javasc