Northwest Business Park is served - i think by the 40D bus (while it remains) - check out
http://www.dublinbus.ie/en/Examples/...rds=Parnell+St. This is going to change sometime in the coming months as part of the way Dublin Bus are changing things. Its a bit of a walk or journey to Parnell Street at the moment, but with the changes coming the 40'd will become cross city buses so going via luas to o'connell street is easier.
Not sure if there are any other easy ways, the 37 bus now goes to Blanchardstown Centre and there may be a local bus from there.
Right now that is the best I can think of.