iTunes will likely pick up on the fact that you didn't buy those songs and refuse to import them. I highly doubt it will delete them.
However, buying an iPod in such a fashion is considered illegal by way of copyright violation. Legally, you're obligated to either pay for copies of those songs, or delete them.
I have an IPOD that I bought used...20gb/4th generation - it has over 2000 songs on it from a previous owner. I've been told that as soon as I attach it to my computer and try to import the songs into ITUNES, ITUNES will know that the songs were not downloaded to my hard drive and wipe them out - is this true? Is there a way to do this without zapping out the ones that came on it already?

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