I just stumbled upon this. I am using NT client. I am sure this should work in 95 and 98 too.
Open your R5 Client.
Open Your R5 Designer.
Shut your R5 Client.
Open your R4 Client.
From your R5 Designer, open any of your applications, open a form design and click Preview on Notes, this will open your R5 Client.
Here you are with both the Clients Open at the same time.