Default Messing With A C550

Hey peeps im new to all the Windows Mobile etc.. as my last phone was a simple sony ericsson :P So now i got a C550 I wanna play around with it change the way it is make it more jazzy as such could anyone help me out bare in mind that the only thing i can do is install a .cab file hehe thanks alot and by the way.. jazzing up can mean new rom , handy files etc.. !

once again thanks!

Dan