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Is there any significant difference between these two cpus? >>
One exists. One does not.

There is no 1700MP. Only a 1700XP. The MP comes in 1.0GHz, 1.2GHz, 1500+ (1.33GHz), 1600+ (1.4), 1800+ (1.53), and 1900+ (1.6).
BOTH the Athlon XP, and newer Athlon MPs come on the new organic (brown cardboard-looking stuff) package. I guess it is possible that they made a few 1700MPs and decided not to sell them as MPs and just released them as XPs? If so, you got a bargain - no, don't return it. What exactly makes you think that you got an MP anyway? Does it say MP on it somewhere? Is it unlocked?
Nack
EDIT: Also see my post in other thread here:
http://forums.anandtech.com/messageview.cfm?catid=28&threadid=616959&STARTPAGE=1