1-Make sure theres no disc in your PS2 and turn it on.
2-Go into memory card settings and delete the frog icon that stands for metal gear online, delete nothing else
3-Put MGO disc in and click on Metal GEar Online option
4-Go to first time
5-Make as many accounts as you want this way
6-write down usernames and passwords so u dont forget
7-reset playstation with no disc in
8-delete the frog icon again
9-Go back into MGO setting
10-Click "Play with detailed settings"
11-choose first option, it shoudl be something similar to play online or something. Its the first option at this screen
12-go through the settings
13-Input Account Manually option
14-follow this step 3 times with your other 3 accounts
15-save all 3 to your memory card when it asks if u want the mto be on memory card list
16-Whenever you wanna log into your memory card accounts
Play using detailed settings->First option->Follow steps normally->choose other option, not "Input Account Manually"->choose your account, log in
17-when u wanna log into your accounts not on memory card, same steps as above except choose input account manually

    Source: geocities.com/gokug614