First you should understand their argments. The bottom line is:Was Muhammad a prophet? When this question is asked by a Jew Muslims will use the following arguments (these arguments were started by Ahmed Deedat and Zakir Naik you should watch their videos for more background on these arguments):
1.They think that Muhammad was the prophet "like Moses" in Deuteronomy 18:18. Obviously anyone who has read the Tanakh knows that the prophet "like Moses" is Moses' successor Joshua (Joshua 1:5, Joshua 3:7, Joshua 3:9)
2. They think Muhammad was mentioned by name in Songs of Solomon 5:16. This is not true. FIrst of all the context is whack, this chapter is talking about sexy people not prophets. Second Muslims will claim the -Im attached to the saidname is a plural of respect like queen elizabeth uses. The plural of respect is only used for God in the Tanakh.
3. They believe that Isaiah 27:29 is a prophesy about an illiterate prophet. If you tell them to read the chapter in context they will see its only referring to the ignorance of a city.
4. They will then claim the Torah and the Tanakh are corrupt. (Muhammad was the first person to invent a jewish conspiracy theory). Tell them about the dead sea scrolls which proves that the script we have today is exactly th same as 2000 years ago. This contradicts Islam because Islam teaches in Sahih Bukhari that the jews changed the text after losing a debate with Muhammad.
Go onto any of the following sites an bring up these points :
www.islam-chat.org,
www.ummah.com,
www.islamicawakening.com,
www.arabchat.org. You may only bring one person out but then this person will continue to spread these points and bring others out. A small difference is still a difference. And it shows them the dont have as much foundation to their religion as they think they do.