Unfortunately, neither Current Journal() nor Maximize Window were available in JMP 4. You could try using the Size Window command to resize the journal window to x pixels wide by y pixels high. You will need a reference to the journal window to make this work. In JMP 4, to get a handle to the journal, you had to save it then re-open it. Here is a simple example:
JSL has advanced so much since JMP 4. I definitely recommend upgrading!
Good luck!
Wendy