When you install I-Deas, it will give you a option to install the ProE Translator in the modules selection box. You have to select this option while installing I-Deas. This will install the tranlator on I-Deas side. In the file export/import menu you now see ProEnginner along with the other options.
There will be a folder named pro in the I-Deas installation directory of your pc. There will be folders called as pro_2001 etc in this driectory along with the Readme file. Go through the readme file and follow the directions as mentioned in the readme. This will complete your installion on the proengineer side. Now you will get an additional menu in the file menu for export/import from/to I-Deas.
Please note that four using this translator, you need to have your Open I-Deas server running on the machine.
As far as assemblies are concerned, you will get the assembly structure into I-Deas but you will not be able to get the constraints transferred.
Regards,
Pratish