We are finding only private guides and they seem quite expensive. Any ideas about how we should go about seeing alot of Berlin in 3.5 days? Maybe part private guide, part group tour??

As an overview you might try this free tour. I know people who have taken their tours in Paris and Munich and reported that they are good. A free overview might help defray the cost of a private guide. I believe you should tip the tour guide.

http://www.newberlintours.com/

Check Context to see if there are tours during your time in Berlin. They are not cheap but they are a good small group tour company. I've used them in Rome.

http://www.contexttravel.com/
http://www.contexttravel.com/city/berlin

Go with Insider tours, or one of the other tour companies in Berlin for a much better tour and probably smaller groups than what the free tours offer. Check them all out and read their reviews on Trip Advisor.

You could also try Jeremy Minsberg, the "Berlin Expert" for good private tour at reasonable costs.

Please avoid New Berlin Tours at all cost. Unfortunately the reason why they have stayed in business for so long is that they do not pay their employees. In fact, the tour guides must pay €3 for every person who attends the tour (even children) and then have to hope that they will earn that money back in tips (they are not allowed to mention this to tour participants though). The company's practices have been featured by several different publications: http://www.thelocal.de/money/20100311-25813.html

I heard a similar rumour about "free" tours in Madrid a couple of years ago.
Berlin Insider provided a thorough walking tour with so much information that it worked out to about 3€ an hour, bargain enough for me.

Thanks for the tip on new Berlin tours. Slave labor? Am thinking about Jeremy minsberg for 1 day and hop on hop off bus for 2 days? What do you think? Also, do you suggest a walking tour? Am not sure we could see enough as we could driving?

As I read about tours, it seems like walking tours cover alot of the sites...must be fairly close together?>

Walking tours are generally concentrated and you don't cover a great geographical area. I did an Insider tour in Frankfurt and we spent 5.25 hours covering a small area. It was a small group that day and we chatted with the guide about whatever we wanted to.