There are many threads about the Facebook application if you search a bit.
On Facebook in the search engine search 'faceook for blackberry' and download the application and upload it via desktop manager.
Hope that helps.
Posted from my CrackBerry at wapforums.crackberry.com
If you're on your BB...the easiest way is to go to mobile.blackberry.com in the browser. Then it should be under (meaning click the link) the "Stay In Touch" link. Its in a short list of social apps for the blackberry. You can then download it OTA (Over the air).