T90CLNT090 vs E61CLNT###

Hi

I am doing exercises in BW courses. In several exercises, Customizing Extractors in T90CLNT090 (in the BI Source System Folder) are required which in turn requires logging in a new 800 client. When I use the user name and password of my BI system access (which has 001 client) I am not able to login.

However, I have access to another R/3 client named E61CLNT### (in the SAP Source System Folder). Can I use this instead of T90CLNT090 to Customize Extractors? Do both of these have same functionalities? If I cannot use E61CLNT### in place of T90, what is the best way to access T90 client?

Thanks in advance

Sundar