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To 'install' IPB, the IPB core files for XOOPS need to be downloaded from the bbpixel website then uploaded via FTP. You need to overwrite, or in some cases add the files manually to the XOOPS core folders.
If you just run the installer (without uploading the files), I dont *think* any existing XOOPS core files will be affected. You should be able to carry on as if you had un-installed any other module.
m0nty is the IPB expert and should be able to clarify this.
If you are looking for an alternative, a new version of CBB (an enhanced version of NewBB 2) is due out soon which has some good forum features. It is a standard XOOPS module so you can install/un-install through admin.