how to change the fonts and color of the text at runtime

hey what i want to do is
i have a format of letter. i want to print this letter in doc format which will also contains some fields from the table. sort of mailmerge application.
So for the fixed data i am preparing xml file. programming i am doing in vb.
now is there any way in which while writing to the doc file i can have some part of the text as bold and of different color. can i set the size of the doc page. (i.e like we have page setup in word)

i am able to write in the doc file but all the data is of same font.

can anyone please help me in this. Thanx in advance.