If you are using OEM, I would instead use the command line import.
I agree that it would be simpler to use the command line. Alter the database from mounted to open and try this:
imp.exe userid=sys@test file=h26b_full.Mar04 log=h26b_full.Mar04.txt show=y rows=n
(You will be prompted for the "SYS" user's password.) This will not actually import data, but it will create a text file showing you what it is in the export. The filename implies that it is a full database export - you might not want all of the users/schemas (in Oracle these are the same thing) that are in it. If it is a full export you will need to create the user account(s) aka schema(s) in Test before import.
Say you only want the "ACCOUNTS" user/schema, you could then import it like this:
imp.exe userid=sys@test file=h26b_full.Mar04 log=accounts.imp.txt fromuser=accounts
("imp.exe" is in "c:\oracle\product\10.2.0\client_1\bin" or similar, depending on your installation.)
This link might be helpful: http://download.oracle.com/docs/cd/B19306_01/server.102/b14215/exp_imp.htm#sthref2573