Database selection, SEO

Question

I am developing a website in ASP.net 3.5 where there is a very big database. I have to show data on one single page dynamically changing from the database and that database will contain data of about 4000 pages having text and images. With formatting tags and lot of tags, its size become huge, So please suggest which database i should use, MS SQL or XML, I don't have any problem ob database size and web space. i have to choose the fastest one,
Due to such a big database, XML data file will also becomes very big, i can't categorize it into separate files, I will use linq for data reterival , Please tell me if big size of XML can make any problem in speed comparing to sql.

 
I have one more problem regarding SEO(search engine optimization), Can google search the data in any one of databases if i will provide the the links, For better SEO, suggest me also, U can also reply me on my mail: [email protected]