If you already own some forum accounts and want to add them to an existing account file, you can just open the account file (extension .sbacc) in NotePad or any text editor and add your entries.

The format of each entry in the account file is as follow:

Forum root|platform|loginname|loginpassword|userid

Example:
http://www.myforum.com/smf|2|testuser|testpass|7

Platform values:
The platform values of an account entry is as follow:
0 = vBulletin
1 = phpBB
2 = SMF 2.x
3 = IPB 3.x
4 = MyBB
5 = SMF 1.x
6 = RESERVED
7 = Expression Engine