1. your current pure tech background has no impact on your future career. u can go for Invst banking anyway as long as u do your MBA courses with rigor and dedication. most of the IIM toppers going to Lehman, Goldman etc were techies/MS in their previous avatars with pure tech exp.
2. Once u get admission in a school u get some time for basics. its better to have a basics overview of accounting, statistics. also brush up basic calculus for economics. dont spend more than a month or 2, 1-2 hrs a day. anyway b-schools conduct immersion sessions pre-course. this is not mandatory and up to you. as of now focus on CAT/GMAT etc.
what is supremely imp is to read bizworld/BT, eco times etc regularly. watch cnbc TV-18 and so on. also some basic fin mags like outlook money to get a hang of terms etc. visit WSJ site to get a hang of wall str.
3.Media line has two career paths...creative and client mgmt. creative parts they prefer non-MBA's. For client mgmt MICA, IIMC, SIMC and similar gets preference. however many media co.s recruit from IIM's and other schools for functions--HR, Fin and so on. starting salaries are usually low in media. chk the link...
http://www.iijnm.org/businessworld.htm