That's completely untrue. Sounds like you need to find a new "computer guy" because this one doesn't have a clue.

Both Windows XP Pro 64-bit and Vista x64 can still run 32-bit applications just fine. There were some hardware issues when Vista first came out, but those have either been resolved or the hardware in question is so old that either most people likely aren't using it anymore/it died from old age/it should probably be replaced anyway.

As for having both a 32-bit and a 64-bit operating system installed at the same time, there's no need for it. If you have either XP Pro 64-bit or Vista x64 installed, you'll no longer need the 32-bit version. 64-bit operating systems can do everything that 32-bit OSs can. Think of it as going from a three string instrument to six strings. It can play all the same songs with the same notes, but now it can play more complex chords as well.

That said, if and when you upgrade from whatever version of Windows you currently have to either XP Pro 64-bit or Vista 64-bit, you will need to reinstall just about all of your software. Unlike upgrading from XP to Vista, you can't go from 32-bit to 64-bit without doing a fresh installation of Windows and thus most of your applications will need to be reinstalled.