I agree with MikeE. The following is just a further clarification with sources and more examples.
My Oxford American College Dictionary says of able that it is the quality of "having the power, skill, means, or opportunity to do something" and that it is followed my an infinitive (able does not require the preposition "to", as Todd says, it requires the infinitive, which is usually coupled with the preposition to).
About capable the OACD says that it is the quality of "having the ability, fitness, or quality necessary to do or achieve a specified thing," which, at first glance, appears to completely synonymous with able. There is a key difference, however, namely that being able to do something requires that we also have the "means or opportunity to do something", i.e. there can be factors in addition to my intrinsic abilities that may affect whether or not I'm actually able to perform the task in question, and I might not be able to perform the task despite the fact that I'm quite capable of doing it. For example:
"I won't be able to pick you up at the airport tomorrow morning [because I have a meeting]."
I am capable of driving to the airport to pick you up – i.e. I have the necessary skills – but am still unable because of previous obligations. Thus capable can't be used in the above sentence. The negative makes the difference even more obvious:
"He's unable to take your call at the moment." (He can't now because he's busy, but in general he is physically and mentally sound and skilled enough to take calls.)
"He's incapable of taking your call." (There's something severely wrong with him that prevents him from operating a telephone.)
The nouns capability and ability tend to be more synonymous than their adjectives, though there might also be small differences there.