Couldn't they attach a rocket to the Hubble and tow it to the International Space Station...?

Sure you could. But for what a price.

1. You would need to do a massive orbit plane change - so you would need a huge rocket. The angle between the two orbit planes is about 30°, so you need a velocity change of 2 * 7.8 km/s * sin(30°/2) = 4 km/s - that is almost half of the velocity change needed for getting it into orbit!

2. On the ISS, the HST is just dead mass, that consumes precious RCS fuel and electricity (for the electrical Control Moment Gyros)

3. It is just a satellite. We have had so many successful space telescopes in history, none of it sits in a museum. The only thing that makes Hubble special is, that until last year it was the biggest space telescope, and that it was kept running by billions of tax payers money for experimental manned maintenance missions. The HST was almost less about astronomy than about experimenting how to work in space.

They have attached something to the Hubble that allows it to be connected to a space ship so it can help maintain its orbit. From what I've heard, though, it would take too much fuel to get it into a safer/self maintaining orbit. Since it costs so much to get fuel into orbit, it would actually be cheaper to build a new telescope and launch it with all new technology.

Since it is too large to fit into any cargo bay, bringing it back to Earth is a no go. Unless that is the final destination, bringing it to the ISS would be fruitless.

As much as I love the Hubble, it's time to let the old girl die peacefully. It's, as posted above, more expensive to maintain it than it is to replace it with a newer one, and now that the Spitzer is functional, and the JWST will be launched in a few years, coupled with the ESA's Herschel space telescope, it's just not needed anymore. The newer ones perform better than she does. It's not financianlly reasonable to save old satellites that aren't needed anymore. The money can be put to better use in the cash strapped space program.

This is theoretically (and financially) impossible. How do we get the rocket into space in the first place? Also, there is no attaching mechanism on Hubble itself; it's only an imaging satellite. There's no way to attach a rocket to Hubble, let alone in space.

In addition to logistics of moving it, there would also be orientation and vibrations issues co-existing with a manned ISS.