Please kindly help if you know solution to this problem. I have downloaded and installed Vmware Server but I keep on getting this message "Login failed due to a bad username or password." when I want to login. Thanks for your help.

The only thing I can tell you is that make sure you have a valid username (with password) enabled for your Windows OS. Virtual Machine uses OS level validation for login. Therefore you can use the same OS username and password for Virtual Machine login.
If you have already done that then perhaps you are facing more complicated issue than that. I would suggest post this problem on Virtual Machine forums.
I am hoping if other members have faced this problem then they would post their solution here.
Hasan