I'm not sure if I'm answering your question, but copyright issues aside, there are several programs which allow creation of loops from any source. Sound Forge (at least up to version 8 - I don't have later versions) has very good tools to make loops that can be used in programs such as ACID, and will maintain pitch and beat information.
If you wish to create a loop inside Vegas, just make a beat-accurate edit in an audio track and then "create subclip." Within Vegas you can then put the subclip on the timeline and stretch it out - seamless loop if your edit is good.
If you are going to use commercial music then you will have copyright issues if you use the music in public. But you can use an application like Cubase to modify loops to fit a time period, but it does take time to learn to use the software.
Watch some videos of how it is done. This one shows what work can be involved.
Yes, that's what I'm looking for...fitting the music to a set time length. Start, bit from middle, and end. I've been doing this manually for years, but thinking there must be affordable software out there by now. Previous software I've tried would only work with it's own created music.