If running Google Apps; as fast as you can get to another computer with a web browser; probably minutes.
If running Microsoft Outlook you have to restore from backups; or if on Exchange configure Outlook on another computer... I'll spare you the details but probably a few hours at least.
Just had a customer have his notebook stolen while on a trip. The data in his outlook PST file plus all his Excel spreadsheets is at risk because it wasn't encrypted nor password protected. Identity and financial information theft is a real possibility. Sure you can use a Windows password, but a tech guy like me can plug the physical drive into another computer and still access all the data unless it was specifically encrypted.
So buy a better notebook with an encrypted drive like this one from Seagate or upgrade to a more expensive version of windows? Or simply pay $50/year and store your documents (even in MS Excel format) on highly secure Google Apps servers using Google Documents?
Google Apps allows all browser sessions to use https. So no data will get transmitted nor stored on the local computer in a usable form for a hacker.
I may sound biased but I'll be recommending the Google Apps solution to my customers. :)