Hi.
That could - COULD - theoretically work if 2 conditions are met:
1) The scanner is attached in some way to your webserver (the Linux machine)
2) You have got commandline scripts that are able to connect to and control the twain driver on the windows machine.
If both conditions are met I think you can use php's commandline execution functions. (based on my assumption that twain can be controlled via scripting at all - but that is beyond my scope of knowledge, so dont cite me there please )
But if you try that you've got some severey interactivity, security and function issues that you'll have to solve... well. Buncha work, so to say.
Don't forget that php is executed on a SERVER and can NOT gain access to resources on a client machine, for the obvious good reasons.
If you need to get stuff scanned and transferred to a server you need some kind of application running on the client - you can do that with java or (in a windows environment) windows application.
That is not possible with php however.
Hope this helps you.
jakob