Sync Notes on iphone with a txt file on windows PC
You have two options:

Using Dropbox, save your files on your Dropbox folder and access them on your iPhone through:


The Dropbox app, tap on a file. I think Dropbox has a built in text editor, or you can select any text-editing app on your device to view/edit it.
Any of the many dedicated text editing apps with built in Dropbox support, such as Elements, Droptext, etc. Look around a bit.


Using iCloud, create notes using the native app. They will be accessible on your PC through:


iCloud.com. Click on mail and select the folder
called "Notes". Note though, you wont be able to edit them just now on this site.
Nonetheless, Apple is supposed to be releasing an update to their
iCloud.com website during the next month or two and give it a
dedicated notes application, which will likely allow for editing
within the web interface. 
Outlook. Install the iCloud Control Panel for windows, and check the box that allows you to syinc notes. Note though, you need a compatible version of Outlook.