Hi santas --
Based on the title of your post we thought you were going to ask about the cost of the MBA - or at least the opportunity cost of taking two years out of your career and foregoing salary for that time - or maybe an existential question about "Is the MBA worth it?" which seems to go around from time to time.
But, happily, it sounds like you're just wondering if you'll be able to pull off a big career switch through an MBA program. And the answer to that is pretty simple: Yes!!
It all depends on YOU of course - nobody gets an awesome new career without a lot of work, both in bschool itself and through networking and all the rest. But with that brief sketch you offered of your background, our guess is that some of the better MBA programs might be very interested in you - your international experience helps a lot, and if you've been at a well-regarded IB (almost regardless of position), then that helps too.
The transition to the two fields you named actually is one of the easier - investment management, for example, is one of the less competitive areas in finance. It's much easier to pull that off, even from an IT background, than it is to go into private equity or some other areas. We've had several clients in the past few years do exactly what you're describing; some of them are currently at Booth, another just finished at Wharton, etc.
The MBA is the ideal vehicle to make the type of jump you want to make. It's not easy, there's lots of hurdles along the way, but it's absolutely do-able.
Hope this helps - let us know if we can give more insights along the way.
EssaySnark
PS: You might try to accelerate your plans for the GMAT - if you don't test until August then you'll likely have to be starting essays at the same time as you're studying - this is not good. Try to get that out of the way in July if you can (provided that you're ready for it of course!).