Without getting all sortsa technical, and assuming you'd prefer not to either, my recommendation would be to forget about RealPlayer and stick with Windows Media Player (and learn to use it to the limits of its capabilities) - their intrinsic capabilities aren't signficantly different - aren't very extensive, either, but they're essentially very similar. Both are primarily playback applications, with some ripping, editing, and burning ability.
That said, for variety of reasons, of the 2 I generally prefer RealPlayer Premium for straight playback,
BUT unless you do a buncha "know whatchyer doin' - and why" fussing when you install
any version of RealPlayer, its gonna be a pesty pain in the butt, with lotsa bundled, well-hidden, tricky-to-remove, generally undesirable companion software, and some irritatingly intrusive habits of its own. Most relatively ungeeky folks are gonna be better off with Windows Media Player. Some web-accessible files won't play in Windows Media Player - for those, you might wanna take a look at
Real Alternative.
If you really want to get in to media manipulation, I suggest you look at dedicated ripping/burning/authoring software, such as that available from
Roxio or
Nero - these aren't players, they're for producing stuff to play and burning it to storage/playback media.