Hi Dhruv - Great questions.
While we can provide some insights, some of these are best directed to the admissions people at the schools themselves - they'll be happy to talk to you about your options and will be a great source for you. Many programs will accept someone without formal HR experience, provided that they do a good job with the personal statements and show how they have transferable skills that are appropriate to HRM. The "HRM or MBA?" question is a common one and you will likely see a bias towards the HRM degree whenever you speak with someone in that industry; sometimes people with MBAs are seen as a little cocky in the business world.
HR people interact with a lot of MBAs and, well ...
What you should do is more research on the types of jobs that you'd be seeking post-MBA, to see if you qualify based on your current background. You'd likely have very good employment opportunities if you want to work in a tech company - many HR people don't have a clue about technology, and your IT + HR could make you VERY appealing to those firms. You would be way ahead of the curve in terms of assessing a candidate's skills and fit to the company because of your training; you would be able to speak the language on both sides of the recruiting relationship, which is pretty rare.
Look around on LinkedIn. See if you can do some informational interviews. The opinions that matter most are those of hiring managers who would be recruiting for the positions you want to have when you're done. If those people have a preference for the HRM Master's - which they might, since they would be HRM specialists themselves - then that's your answer.
Another opinion that would matter though would be the COO, if you can get access to them - they'd be in the best position to say if they want an HR person who has specialized in HR, or an HR person who knows business.
The main reason we'd say that the HR Master's could be more useful is simply because you'd be coming in cold. Given the lack of focus on HR in most bschools, you wouldn't get the same type of exposure to best practices and the body of knowledge in an MBA program.
All that being said: There's some decent bschools with good HRM degrees, including schools like Mays in Texas and Vanderbilt Owen;
wikipedia has a list you can start with.
Important note: You need to be well aware of the economic realities. Many HR professionals don't have a master's at all, one reason being that the HR field just doesn't pay that much. It's also often a dead-end career; it's very rare that someone advance through HR up to the executive suite. In fact,
an article from Forbes last year put the Master's in HRM as #10 on their list of worst graduate degrees. You may have trouble recouping your costs through this path; the financial ROI is not nearly as strong as with a more traditional post-MBA career (consulting/finance/etc.).
Hopefully that doesn't deter you - you sound like you're inspired to make a difference. We would encourage you to also explore the field of Organizational Behavior which is taught in the core curriculum of most MBA programs; it's related to HR but much different.
Happy to offer additional insights if we can, feel free to post again.
EssaySnark