|VLAN's are by definition, separate from each other.|
If your VLAN's have separate subnets and you do not create static routes between those subnets (VLAN's) then they can't cross communicate.
From the sounds of it, you don't really understand VLAN's and VLAN tagging and I highly recommend you spend a little time doing some reading/research on VLAN's before you begin.
I'm a little confused about how to configure it in the Cisco 3750 switches. Can any-one give me some guidance ???
Again, it's better to know what you're doing before starting out to do something than it is to try and figure it out on the fly. My recommendation for you is to hire a qualified professional to help you get everything setup.
Left to your own devices, and taking into consideration your level of knowledge, you're more likely to make a mess of things than you are to successfully set it up.
I'm not saying this to put you down or disrespect you, I'm simply pointing out a fact and attempting to give you some good advice which should save you time and therefore, money.
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.