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Further adding to the post above, the 3000+ / 3200+ will have 3000+ / 3200+ written on the box, so you should have no trouble in identifying models. Its only for identifying the Venice that you should check the above post.
As for identifying DDR400 RAM, AFAIK there isnt any way to simply look at a RAM module and identify its speed. You'd need to trust your dealer on that . Else you could check the IC Part numbers on the RAM module, come home access the net and check the manufacturer website for more info on that Part number.
Else just buy branded ram such as Twinmos/Transcend. These have a sticker on top of the RAM chip which lists the speed. I suggest twinmos as its not much more expensive and overclocks nicely as well.