I studied abroad in Australia for a semester, so this may not apply much at all, but just in case:
I went to a pretty pricey private school here in the states, so going abroad was fueled by 2 factors.
1) Price. It's usually cheaper to study abroad as long as you do direct-enrollment at a foreign university instead of a program (although this is usually dependent on how well your university's study abroad office is).
2) Experiencing the world outside the "ivory tower" that US universities cultivate.
Not only did I get both of those benefits, I greatly enjoyed it. I would definitely recommend doing direct enrollment. While foreign programs do greatly simplify thing, you usually end up living in a conclave of American students in a foreign atmosphere, which pretty much goes contrary to the whole "study abroad" experience (plus you pay US university rates, which suck). In my school, most students went abroad first semester of their 3rd year, but lots of students also did a whole year with a few doing a single semester their 2nd semester of 2nd or 3rd year. If you're looking to eventually live there, doing a whole year abroad is probably the best way to go.
The administrative stuff is almost always really simple. Most foreign schools of any decent caliber have a program whereby foreign students can apply for a semester or longer, and once you get accepted into one getting a visa is incredibly simple.
Specific to England, I'd say almost a third of the kids I know who studied abroad went there, so it might be the hardest to get into. That being said, I know a couple kids who studied abroad for a full year, then went back over there to work after they graduated. I don't know if it was because of contacts they got while living over ther, but I imagine it didnt' hurt. I'd say study abroad, direct enroll in a school, and try and find a space to live surrounded by English students near your university. Keep in touch and you'll at least have a few friends to shack up with if you plan on going back.
Any specific questions you might have I can address, so just let me know.
Forgot to add, I did have to pay a fee to hold my spot in my school back home, but the whole experience (fees + tuition + living + travel) was cheaper than a single semester back home, so make sure you take that into account.
