you should be able to pull up all the keys from the keyboard, carefully though, as they have little attachments. Pull them up and clean them and underneath and it should be ok; remember though to put them back in the same order lol

While I was in Iraq last year, Iwas part of the technical maintenance section for the south eastern division.

We had a lot of laptops come in occasionally with this problem, we'd normally dismantle them to clean them out, but from time to time this was impossible, what we used to do was use some methonol as it evaporates quickly it doesn't damage anything, I think thats your best bet.

The desktop keyboard keys are easier to remove. Sometimes the longer keys such as the space bar are attached at two places, so watch out.
If you spill sugary liquid, such as coffee or soft drinks, dry out as much as possible with tissue or blotting paper to minimise the deposit of sugar.
In the worst case, I believe there are some USB keyboards in the market, if they work as a replacement.
Good luck.

This happened to my firend at university. He spilt a bottle of wine on it and it damaged the keyboard. If its just a problem of the keys sticking, then it shouldn't be too hard to clean, maybe try taking it into a PC repair shop if you can't do it yourself. However if the liquid has effected the electronics of the keyboard (as it did with my friend's) then as Mathpath mentioned, you can easily just stick a USB keyboard in it. (Although this may look a little silly on the train!)