A variety of things could be causing the slow startup. The first place I would look is at the Login items on your MacBook to see if there are items in this list that are set to automatically start. Having applications automatically start will increase startup time. This article has the steps to do this:
The steps from the article should work for Mac OS X 10.4-10.8; the only difference in Mac OS X 10.7 and 10.8 is that the Accounts icon is named Users & Groups:
To permanently prevent items from opening at login:
- Choose Apple menu > System Preferences, and then click Accounts.
- Click Login Items.
- Select any items you don’t want to open automatically, and then click the "-" button.
If you are still experiencing a slow startup after that, you might want to try the steps in the following article:
I hope this helps!