I used to use Parallels to run Windows, but I ran out of uses for Windows, so let that lapse. I did recently have a need for IE7 (don't ask, but I'm looking at you, Business Objects) and installed XP using VirtualBox and it's peachy and cost no money (I have an old OEM XP licence). I actually run the VM off a USB disk and it's still obscenely perky for an XP machine, though it hasn't had time to clutter. Anyway, it's a nice inexpensive solution that should meet your requirements to run legacy Windows software under MacOS. It supports copy and paste, seamless mouse and keyboard integration etc.
Long term though, you ought to look at migrating to newer software. I know it's a pain, but one day you'll find they no longer work. Trust me, I get calls to this day about software we discontinued a decade ago and they've discovered that after a systems upgrade that it doesn't work and, oh, 'help!
(Note that if you run Windows as VM, you should ensure it's secure – MS Security Essentials is perfectly adequate.)