Several people have described me as 'intelligent' because of my ability to to research and answer some of the more obscure questions here on AB. Unfortunately, I'm not smart enough to work out how to make any money out of my (so-called) intelligence ;-)
If you'd prefer a more 'academic' definition, the Concise Oxford Dictionary defines 'intelligent' as 'having or showing (usually a high degree of) understanding; clever, quick of mind'. (The word is derived from the Latin for 'to understand')
The definition of 'smart' embraces that of 'intelligent' but offers alternative, or additional, meanings. For example, it can mean 'clever' or 'ingenious' but it also means 'keen in bargaining' (which is probably a compliment) or 'quick to take advantage' (which is probably not a compliment).
In some circumstances 'smart' can go beyond 'intelligent'. For example a 'smart employee' is defined as one who is not simply 'intelligent' but 'ready and intelligent'. That, of course, assumes that a completely different definition of 'smart' isn't being used. A 'smart employee' might simply be an employee who always starches his collars and polishes his shoes ;-)
Chris