How do I know when fermentation is complete?

My knowledge of brewing is not very extensive. I've basically just followed the instructions to complete a couple of brews, which says to let the batch ferment for 2 weeks in the 5 gal. fermenting bucket that came with the kit. There is a percolator on top which I use as an indicator. Right now I have an IPA going...it bubbled hard for the first day or two of fermentation, but now, day 5, its all but stopped. What are your recommendations on when to bottle the batch? Should I allow it to go the whole 2 weeks or can I bottle early?

Next time you brew, you should use a hydrometer. This will be a very useful tool in determining when your brew is done. For this batch, I would wait at least 10 days. If you see no airlock activity for a day or so, you should be safe to bottle.

You could get a hydrometer now. If readings don't chance for a few consecutive days, it's done.

If you have another bucket, this would be a good time to rack it to a secondary(off of the trub). That will usually shake the yeast up a little and stimulate more activity. If you don't get a hydrometer and you don't have a secondary, make sure that your temperatures aren't below 68 degrees or so, give the bucket a gentle rocking(no splashing!) and let it go for 10 days.
Low temps can slow fermentation to a crawl. The danger there is that the brew gets bottled and eventually overcarbonates or explodes. Good Luck.