Vista - Help getting software installed

My wife and I got brand new computers a couple of days ago, installed with Vista Home Premium x64. She spent 2 days getting her software re-installed, but mistakenly loaded an old version of a program. She uninstalled it, but when she tried to install the correct version, it comes up and says it's got the wrong registration number (ie. the one from the old version). We've cleared out everything that we can think of, from leftovers in the Roaming directory to searching through the registry for any sign of the software that we could think of and systematically removed it, but... no go. We even used the Microsoft Live Scan registry scanner to find leftover entries.

Any ideas how we can figure out where this data is, other than reloading the entire system and destroying many hours of work? We'd both be eternally grateful.

Most commercial software that has licensing has a forum(unless it's extremely simple software) and chances are good somebody else using that product had the same issue and can tell you how to restore the proper version.

Try google of product name and user forum