My downloads/streaming videos are getting cut off midway, normally after a couple of minutes for no noticeable reason. I'm fairly certain it's my cheapo router. It came and went a few months ago and it seems to me that if it was my router it'd be a persistent problem.
Anything else it could be? (software? modem?)
Any way to tell what's causing it?
And, most importantly, how to fix it?

Flash your router with a newer version of firmware.

I've seen some pretty bizarre and hard-to-find behaviour out of home routers. They're the no.1 bane of nerds everywhere; I hate the things.

Firmware. Why didn't I think of that?
The only problem is Philips haven't released an updated firmware.
I suppose that's what I get for buying the shit they peddle to you at PCworld.

Take the router offline and connect directly for a few hours. Download and stream lots of stuff. If the problem doesn't persist during that time, you can be sure it's the router. If it is, replace it with something decent.

Just make sure your computer is locked down and secure before you do this.

Thanks for the advice, I fixed the problem.
I have two computers one Windows with a static IP and one Linux using DHCP. I gave the Linux one a static IP and the problem is fixed. ~