I am a Christian - Baptist (Independent). If you want clarification on what my particular beliefs are, perhaps I'll figure out the journals thing to put that up.
In my opinion, the tree is not a Christian symbol. Sure, people have given it such symbolizm now, but I do not accept it. (Besides, there are other things given Christian symbolizm that are blatently not.)
Since Christmas is really Christ-Mass, it is just another way of saying church service... it just focuses on the fact that it is a service about Christ. Technically, I go to a Christ-Mass every Sunday.
However, Christmas is traditionaly considered Jesus' birthday. (Although, he wasn't born in December, from what I understand.)
A proper symbol is the Nativity (manger scene), though the normaly displayed ones tend to have some inaccuracies, but that isn't important.
Now, when it comes to religious based lawsuits, there are probably situations that it is okay... but usually, I'd say no. Since I don't consider a decorated tree to be a proper Christian symbol, I don't mind other religions protesting it.
It does look good, and makes public property look better too.
I celebrate Christmas primarily by going to my church's candlelight service that is geared to focusing on the birth and ministry of Jesus.
After that, we do exchange presents. However, if I should ever get married and have kids, I don't want to do Christmas presents. I'd rather have random presents during the year. I could suddenly come home in April with a board game, a video game and a gorgeous piece of jewlery for my wife... all for no apparent reason.
Well, back on topic:
Launching a religious lawsuit does more to hurt the religion of the one launching it then it does to the religion under attack.