Ah the barre's, I remember this from being a beginner. My friend who taught me built me up to them by having me play the chord without the index finger to begin with and then introducing it later. Let me see if I can draw this to make it easier....my head's in f minor from what I've been playing tonight so let's use that chord:

E-1------
B-1------
G-1------
D-----3--
A-----3--
E-1------

What I used to do to begin with was:

E--------
B--------
G-1------
D-----3--
A-----3--
E--------

and then

E--------
B-1------
G-1------
D-----3--
A-----3--
E--------

using the index finger on the G and B strings and then later I built up to the first chord I gave.

Move that shape up and down and you'll find there are cetain frets that make it easier to finger because the stretch isn't so big. Try playing d minor on the 10th fret with that shape and you'll see what I mean. Practice that shape all the way up to 12 and beyond if you find your bear-paws aren't too big to go beyond that. I've got quite thin fingers so I can and I've made a few friends jealous that way.

I started on a beat up old acoustic I borrowed from school and when i made the switch to electric when I could afford one I found it paid off because barre chords were automatically easier. I've been reading Keith Richards's autobiog lately and he advocates this approach too, but if you've already got an electric then use it, it's the same in theory but just feels different. You'll find practising on an acoustic will give you firmer and more certain fingering when you play electric. I still find myself having to adjust technique slightly, especially when picking a barre chord - if I've been playing my acoustic and then go electric and strike a big chord like that I find it sounds horrid to start with (especially if I'm playing with a pick) but it just takes a minute of warm-up to adjust how I strike the strings.

Don't change your string gauges on your acoustic, 12-54's pretty much the standard set.

If your hands are big enough there's another trick you can try (again this comes from my friend, he loved this and never used the index finger to barre himself, but I don't really find I do it unless my hands are tired): Try using your thumb to finger the note on the low E string - this is often called the 'baseball bat' technique. When I play chords like that I often leave out the top note on the high E altogether although you can play it by covering B and E with the index finger - I just don't out of personal preference. I do this a lot more on electrics than my acoustic although I had to wait a couple of years for my hands to be big enough when I first started.