I do not know if the “DSO BenF v3 for IAR5.0.rar” has ever been reported to work correctly on IAR 5.0. There were some extra patches (by Antonio) to make it work in the svn repo which disappeared.
My git tree includes fixes for the same issues as Antonio was working on, so except for the __iar_program_start rename (which I will fix soon) it should work.
EDIT: Fixed up the git tree for IAR 4 and IAR 5 (untested). Feedback welcome.