Finally, I found out a way to use msn on Pearl 8100 using Gtalk. It's free!
First download and install PSI on your PC, add your gmail account, and login.
Then in PSI, register your msn account.
You will find that your msn contacts will be added into your Gtalk. Then close PSI on your PC, also this is all what you have to do on your PC. (search "PSI msn" for more details)
Now you go to your 8100, login Gtalk, you will see all msn contacts in your list. First time you will get many email in your gmail, don't care.
Ok, enjoy your msn on your Pearl 8100!!! Actually it's Gtalk.