You don't need a new username or password ,if you are able to connect your Blackberry to your Work Desktop and manually generate an encryption key by following below steps :- Its called a Wireline Enterprise Activation
(Only if you are either connected to you LAN directly or using VPN)
1)Open Desktop Manager (if you dont know what Desktop Manager is ,wait for ur password

)
2)Open Redirector Settings
3)Open Security Tab
4)Change Generate Encryption Keys mode to Manual
5)Click on generate keys
6)Move mouse
7)Hit apply ,till the status goes upto date
Repeat step 5,6,7 again 2 more times.
NOTE :If using Outlook 2003,disable Exchange Cache Mode from account settings.( if not sure how to do this Google it)