Multi DB and get_last_updated();

Hi, I would like to install Multi DB for my wpmu blog/s but I have a compatibility doubt:

I need to use get_last_updated for publish on the main site the last post of the blogs.
(here the link:
http://wparena.com/how-to/how-to-get-posts-from-all-blogs-in-multi-site-network/
)

Are they compatibility?
Do you have a plugin that do the same?
Do you know where i need to insert (in what file) the get_last_updated code?

thanks