I need to make an important decision about this:

In my new webForum, I will have polls.

If I save the pollVotes in DB I'll have a thousand of rows(votes) in a few days!

Suppose, if I have 40 polls and 300 users I'll have:
300x40 = 1200 rows

My table is: (PollID int, MemberName nvarchar(256), PollChoice int)

In a couple of weeks/months I'll have my database size INCREASE!

I'm wondering:
Save this votes into a xml file is a good choice? Is it fast?
I never worked with xml. I don't want to know how can I do it but I need to know the philosophy.
I can save a xml for each poll.
I only need to know If I can add more nodes into an xml file without
need to take all nodes into aspnet, add one more and then resave all nodes.

second question:
When a user come to a pollThread he need to now how mani users voted in choice1, choice2, ...
Can I count fast the nodes who have attribute("choice=1"), attribute("choice=2"), attribute("choice=3"), etc...

I'll appreciate any comments about this idea!
Thanks