Depends... Dutch staff will most likely take you on board, Belgium or French staff won't.
There is a Amsterdam tourist card (Available from Schiphol ticket window) if I recal correctly which allows for 24, 48 or 72 hour of unlimited public transport in Amsterdam including your rail transfer.
Sloterdijk can be used on the lower level during the afternoon for trains coming from Centraal towards Zaandam.
http://www.flickr.com/photos/denniskoster/7321405938/in/photostream
A 15 minute walk will take you at one of the harbour shunt locations:
http://www.flickr.com/photos/69841044@N02/8078869098/in/photostream
If you want a decent shot of a Fyra try Hoofddorp (5 minutes from the airport)
http://www.flickr.com/photos/18markrijs/5640414597/ Here all through trains to the HSL and Leiden will use the avoiding lines.
Want something classic? No worries... A few times a day (DB Night trains) will be shunted into the station by Class 1200
http://www.flickr.com/photos/hvondelen/5843088943/in/pool-1298240@N24/
There are three of the class selected for this duty's so it does pay of to come back a few times. Another location is Muiderpoort:
http://www.flickr.com/photos/peter_boere/5523228828/
Do and Don't
Do: Walk through the red light district and do it slowely.
Don't: Get in. Especially not in de Bloedstraat, these are not ladies but something in between. It might sound weird, but the RLD is the safest area in Amsterdam.
Do: Hire a bike. IGNORE red lights.
Don't: Go to Amsterdam West or South (Like Bijlmer) especially not after dark.
If you have any questions please ask, I work in Amsterdam and live 20 minutes away so I know my way around.