In both Sametime and Connections builds I have come across customers installing different versions of Installation Manager than that recommended or supplied with the product. The ST and Connections apps are both 32bit so although they will install under a 64bit version of Installation Manager, you will get a warning about it being 64bit. Don’t ignore that.
There’s no advantage to you choosing 64bit Installation Manager over 32bit on a 64bit platform and worse, since it manages all your installs, if you discover it’s a problem later you can’t fix it because you can’t uninstall it without uninstalling everything it installed itself. I did a workaround at a customer I was brought into once where we renamed the IM folder and installed a new 32bit version to make sure ST Media Manager would install but that’s a fudge.
Do yourself a favour, you can’t go wrong with 32bit 🙂