Yes...
fairly simple, you just edit this line in your php header before any html:
query_posts('showposts=6'); //how many posts to display on page
to query the categories also. you can query the categories via the category id or the name, query mutliple categories, and query post NOT in a specific category as follows:
category_name=black 2 colour //returns posts in category called "black 2 colour "
cat=1 //returns posts in category ID 1
cat=-1 //returns any post NOT in category ID 1
cat=2,6,17 //returns all posts from categories with ID either 2,6,17
just use an ampersand to seperate multiple queries (ie how many posts to display and from which categories)
for example:
query_posts('category_name=Uncategorized&showposts=3');
or
query_posts('cat=1,3,5&showposts=12');
(you can also query your tags, with the code tag=TAG_NAME for example
query_posts('tag=digital&showposts=6');
would return the 6 latest posts tagged with 'digital'
...
infact theres a huge amount of queries you can run if you understand a little php, with guide and examples here)
hope that helps
Ciarán