how can i access other computers on my lan that are in a different workgroup?

Answer 1

if you have the administrator password then you can do it
depends on what you are trying to do

Answer 2

If you have connection to other computer it should be no problem
Of course you also need the User and Password for PC you connect to.
1. Check connection using DOS command
c:\> ping 12.34.56.78 Example only

if reply ok its mean got connection

Answer 3

if there is no ping to that computer ( different network ) add route either to that PC or to that network

Good luck