you can root your phone. this will give you more control over your phone (superuser permissions), allowing you to tweak a lot more stuff (theming, overclocking, etc.).
one of the biggest perks of rooting is the ability to flash a custom rom. the vibrant doesn't have a huge dev base, but i'm pretty sure there is a froyo rom (cognition, i think it's called?). so in short, yes, it is possible to unofficially get froyo onto your phone.
