First of all thanks to these bloggers:
Most important thing to remember :
As I have already pointed out that Videocon Zeus V7500 is clone of Commtiva Z51 and it lacks trackball.All ROM's you may find on net are developed for Z71. As result most default recoveries are unusable with V7500 because most of them require selection of item by pressing trackball. So we may use clockworkmod z71 recovery (for boston, z71 and clones),which is the only one other than stock recovery which I found to work with V7500. Also it is important to keep in mind that at any given point either the recovery or the rom(android os)should be in working condition to avoid possible brick.If both work then its better.
I'm using 64 bit Windows 7.
Also enable USB debugging on your device from"settings->applications->development"
I assume that we have official 2.1 ROM installed. First we need to root the device. z4root1.3(get it from 4shared.com) will do the job. First we will backup the official recovery.
When you connect you phone to PC you will see some thing like this.Also click OK if it promts to run setup.exe. Open and copy the contents of this drive to some folder, for example folder named "driver" in our case. So if you put the folder named "driver" in your D drive; you will do cd d:\driver in command window(run cmd on windows).
This is just to give an idea. it is running on 2.2.1
To run the adb run command:
you will see message that some is service is starting.
now use su to get superuser access. You will need to provide access on your phone, so keep an eye on your device as you enter su command.
Also disable USB storage. You should not be able to see your sdcard.
to see partitions on your phones
cat /dev/mtd/mtd3 > /sdcard/recovery.img
to backup recovery partition on sdcard.You will have recovery.img file in root of your sdcard, backup the file in some safe place.
Now download rom manager from market and install clokworkmod recovery for Boston,Commtiva z71 clones. Power off the phone and restart by pressing camera+vol.up+power to get in recovery mode, press camera button forcefully or you will have normal boot. Once in recovery mode we will backup our stock ROM. Clokworkmod is designed for z71 i.e trackball so when we use any key it behaves bit oddly in Videocon Zeus. One key press is registered twice. So if we are on menu item no.1 and want to go on menu item no.2 by pressing vol.key only once, we will actually go to menu item no.3 in clockworkmod recovery. Work around this is to simultaneously press both vol up+vol.down keys. Just try few times you will get to know how it works. We press green button(call receive)button to select menu item. Now it is also registered twice. So when u press green button you automatically end up running first item on the sub-menu. Workaround it is to keep holding atleast one key till you have reached desired menu item. So to select second item on submenu you will browse to desired item on the main menu using vol. keys. keep holding volume key and press green key. As soon as you press green key you keep holding it and leave the vol.keys. Now browse submenu using vol.keys. Try it you'll understand what i'm trying to explain.
Now backup your stock ROM using appropriate selection in clockwormod recovery. Copy this recovery files from sdcard and keep it in some safe place on your hard drive or burn to cd.