Well, your 1.7 isn't going to get very high at all. At 1.79v, mine manages about 1950 before giving up the ghost and bombing me back to POST. Given, it's in a crappy board not made for overclocking, but hey, I can't complain about the price I paid for it. If the board is an 845PE board, and has some reasonable features, and is at a good price point, I say go - you could always sell the CPU for a couple bucks to someone who won't use it as avidly as an enthusiast would.
They are, in fact, stripped down Willamette core P4s with half the cache. .18 micron, default 1.75v - neither of which is very conducive to getting much above 2GHz, which the Celeron desperately needs to keep up in newer games with even the slowest of Athlon XPs... but if the system isn't for gaming or anything intensive, you don't need the clock speed, and the free CPU will work just dandy.